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2http://en.wikibooks.org/wiki/Computer%20programming%

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3http://en.wikibooks.org/wiki/Computer%20programming%

2FStructured%20programming

4http://en.wikibooks.org/wiki/Open%20Source

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uton

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tions

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es

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2FCreating%20Python%20programs%2FSolutions

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asic

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33

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ceis

dist

inct

from

nam

esou

tsid

eof

the

nam

espa

ce.

Thi

sla

yeri

ngof

nam

espa

ces

isca

lled

scop

e.A

nam

eis

plac

edw

ithin

ana

mes

pace

whe

nth

atna

me

isgi

ven

ava

lue.

Fore

xam

ple:

>>>

dir()

['__builtins__',

'__doc__',

'__name__']

>>>

name

="Bob"

>>>

import

math

>>>

dir()

['__builtins__',

'__doc__',

'__name__',

'math',

'name']

Not

eth

atIw

asab

leto

add

the

"nam

e"va

riabl

eto

the

nam

espa

ceus

ing

asi

mpl

eas

sign

men

tsta

tem

ent.

The

impo

rtst

atem

entw

asus

edto

add

the

"mat

h"na

me

toth

ecu

rren

tnam

espa

ce.T

ose

ew

hatm

ath

is,w

eca

nsi

mpl

y:

>>>

math

<module

'math'

(built-in)>

Sinc

eit

isa

mod

ule,

ital

soha

sa

nam

espa

ce.T

odi

spla

yth

ena

mes

with

inth

isna

mes

pace

,we:

>>>

dir(math)

['__doc__',

'__name__',

'acos',

'asin',

'atan',

'atan2',

'ceil',

'cos',

'cosh',

'degrees',

'e',

'exp',

'fabs',

'floor',

'fmod',

'frexp',

'hypot',

'ldexp',

'log',

'log10',

'modf',

'pi',

'pow',

'radians',

'sin',

'sinh',

'sqrt',

'tan',

'tanh']

>>>

Ifyo

ulo

okcl

osel

y,yo

uw

illno

tice

that

both

the

defa

ultn

ames

pace

,and

the

mat

hm

odul

ena

mes

pace

have

a'_

_nam

e__'

obje

ct.

The

fact

that

each

laye

r

can

cont

ain

anob

ject

with

the

sam

ena

me

isw

hats

cope

isal

labo

ut.T

oac

cess

obje

cts

insi

dea

nam

espa

ce,s

impl

yus

eth

ena

me

ofth

em

odul

e,fo

llow

edby

ado

t,fo

llow

edby

the

nam

eof

the

obje

ct.T

his

allo

wus

todi

ffer

entia

tebe

twee

nth

e__name__

obje

ctw

ithin

the

curr

entn

ames

pace

,and

that

ofth

eob

ject

with

the

sam

ena

me

with

inth

emath

mod

ule.

Fore

xam

ple:

>>>

print__name__

__main__

>>>

printmath.__name__

math

>>>

printmath.__doc__

This

module

is

always

available.

It

provides

access

to

the

mathematical

functions

defined

by

the

Cstandard.

>>>

math.pi

3.1415926535897931

6D

ata

type

s

Dat

aty

pes

dete

rmin

ew

heth

eran

obje

ctca

ndo

som

ethi

ng,o

rwhe

ther

itju

stw

ould

notm

ake

sens

e.O

ther

prog

ram

min

gla

ngua

ges

ofte

nde

term

ine

whe

ther

anop

erat

ion

mak

esse

nse

fora

nob

ject

bym

akin

gsu

reth

eob

ject

can

neve

rbe

stor

edso

mew

here

whe

reth

eop

erat

ion

will

bepe

rfor

med

onth

eob

ject

(thi

sty

pesy

stem

1is

calle

dst

atic

typi

ng).

Pyth

ondo

esno

tdo

that

.Ins

tead

itst

ores

the

type

ofan

obje

ctw

ithth

eob

ject

,and

chec

ksw

hen

the

oper

atio

nis

perf

orm

edw

heth

erth

atop

erat

ion

mak

esse

nse

for

that

obje

ct(t

his

isca

lled

dyna

mic

typi

ng).

1http://en.wikipedia.org/wiki/Type_system%23Type%20checking

43

Pyth

on's

basi

cda

taty

pes

are:

•In

tege

rs,e

quiv

alen

tto

Clo

ngs

•Fl

oatin

g-Po

intn

umbe

rs,e

quiv

alen

tto

Cdo

uble

s•

Lon

gin

tege

rsof

non-

limite

dle

ngth

•C

ompl

exN

umbe

rs.

•St

ring

s•

Som

eot

hers

,suc

has

type

and

func

tion

Pyth

on's

com

posi

teda

taty

pes

are:

•lis

ts•

tupl

es•

dict

iona

ries

,als

oca

lled

dict

s,ha

shm

aps,

oras

soci

ativ

ear

rays

Lite

rali

nteg

ers

can

been

tere

das

inC

:

•de

cim

alnu

mbe

rsca

nbe

ente

red

dire

ctly

•oc

tal

num

bers

can

been

tere

dby

prep

endi

nga

0(0

732

isoc

tal

732,

for

exam

ple)

•he

xade

cim

alnu

mbe

rsca

nbe

ente

red

bypr

epen

ding

a0x

(0xf

fis

hex

FF,o

r25

5in

deci

mal

)

Floa

ting

poin

tnum

bers

can

been

tere

ddi

rect

ly.

Lon

gin

tege

rsar

een

tere

dei

ther

dire

ctly

(123

4567

8910

1112

1314

1516

1718

1920

isa

long

inte

ger)

orby

appe

ndin

gan

L(0

Lis

alo

ngin

tege

r).C

ompu

tatio

nsin

volv

ing

shor

tint

eger

sth

atov

erflo

war

eau

tom

atic

ally

turn

edin

tolo

ngin

tege

rs.

Com

plex

num

bers

are

ente

red

byad

ding

are

alnu

mbe

rand

anim

agin

ary

one,

whi

chis

ente

red

byap

pend

ing

aj(

i.e.1

0+5j

isa

com

plex

num

ber.

Sois

10j)

.N

ote

that

jby

itsel

fdoe

sno

tcon

stitu

tea

num

ber.

Ifth

isis

desi

red,

use

1j.

Stri

ngs

can

beei

ther

sing

leor

trip

lequ

oted

stri

ngs.

The

diff

eren

ceis

inth

est

artin

gan

den

ding

delim

iters

,and

inth

atsi

ngle

quot

edst

ring

sca

nnot

span

mor

eth

anon

elin

e.Si

ngle

quot

edst

ring

sar

een

tere

dby

ente

ring

eith

era

sing

lequ

ote

(')or

ado

uble

quot

e("

)fol

low

edby

itsm

atch

.So

ther

efor

e

'foo'

works,

and

"moo"

works

as

well,

but

'bar"

does

not

work,

and

"baz'

does

not

work

either.

"quux''

is

right

out.

Trip

lequ

oted

strin

gsar

elik

esi

ngle

quot

edst

rings

,but

can

span

mor

eth

anon

elin

e.T

heir

star

ting

and

endi

ngde

limite

rsm

usta

lso

mat

ch.T

hey

are

ente

red

with

thre

eco

nsec

utiv

esi

ngle

ordo

uble

quot

es,s

o

'''foo'''

works,

and

"""moo"""

works

as

well,

but

'"'bar'"'

does

not

work,

and

"""baz'''

does

not

work

either.

'"'quux"'"

is

right

out.

Tupl

esar

een

tere

din

pare

nthe

sis,

with

com

mas

betw

een

the

entr

ies:

(10,

'Mary

had

alittle

lamb')

Als

o,th

epa

rent

hesi

sca

nbe

left

outw

hen

it's

nota

mbi

guou

sto

doso

:

10,

'whose

fleece

was

as

white

as

snow'

Not

eth

aton

e-el

emen

ttup

les

can

been

tere

dby

surr

ound

ing

the

entr

yw

ithpa

rent

hese

san

dad

ding

aco

mm

alik

eso

:

('this

is

astupid

tuple',)

Lis

tsar

esi

mila

r,bu

twith

brac

kets

:

['abc',

1,2,3]

Dic

tsar

ecr

eate

dby

surr

ound

ing

with

curl

ybr

aces

alis

tof

key,

valu

epa

irs

sepa

rate

dfr

omea

chot

herb

ya

colo

nan

dfr

omth

eot

here

ntri

esw

ithco

mm

as:

{'hello':

'world',

'weight':

'African

or

European?'

}

Any

ofth

ese

com

posi

tety

pes

can

cont

ain

any

othe

r,to

any

dept

h:

((((((((('bob',),['Mary',

'had',

'a',

'little',

'lamb']),

{'hello'

:'world'

}),),),),),),)

7N

umbe

rs

Pyth

onsu

ppor

ts4

type

sofN

umbe

rs,t

hein

t,th

elo

ng,t

heflo

atan

dth

eco

mpl

ex.

You

don’

thav

eto

spec

ify

wha

ttyp

eof

vari

able

you

wan

t;Py

thon

does

that

auto

mat

ical

ly.

•In

t:T

his

isth

eba

sic

inte

gert

ype

inpy

thon

,iti

seq

uiva

lent

toth

eha

rdw

are

'clo

ng'f

orth

epl

atfo

rmyo

uar

eus

ing.

•Lo

ng:

Thi

sis

ain

tege

rnu

mbe

rth

at's

leng

this

non-

limite

d.In

pyth

on2.

2an

dla

ter,

Ints

are

auto

mat

ical

lytu

rned

into

long

ints

whe

nth

eyov

erflo

w.

•F

loat

:T

his

isa

bina

ryflo

atin

gpo

intn

umbe

r.L

ongs

and

Ints

are

auto

mat

i-ca

llyco

nver

ted

toflo

ats

whe

na

float

isus

edin

anex

pres

sion

,and

with

the

true

-div

isio

n//

oper

ator

.

49

•C

ompl

ex:

Thi

sis

aco

mpl

exnu

mbe

rco

nsis

ting

oftw

oflo

ats.

Com

plex

liter

als

are

wri

tten

asa

+bj

whe

rea

and

bar

eflo

atin

g-po

int

num

bers

deno

ting

the

real

and

imag

inar

ypa

rts

resp

ectiv

ely.

Inge

nera

l,th

enu

mbe

rtyp

esar

eau

tom

atic

ally

'up

cast

'in

this

orde

r:

Int→

Lon

g→

Floa

t→C

ompl

ex.T

hefa

rthe

rto

the

righ

tyou

go,t

hehi

gher

the

prec

eden

ce.

>>>

x=

5>>>

type(x)

<type

'int'>

>>>

x=

187687654564658970978909869576453

>>>

type(x)

<type

'long'>

>>>

x=

1.34763

>>>

type(x)

<type

'float'>

>>>

x=

5+

2j

>>>

type(x)

<type

'complex'>

How

ever

,som

eex

pres

sion

sm

aybe

conf

usin

gsi

nce

inth

ecu

rren

tver

sion

ofpy

thon

,usi

ngth

e/o

pera

toro

ntw

oin

tege

rsw

illre

turn

anot

heri

nteg

er,u

sing

floor

divi

sion

.Fo

rex

ampl

e,5/2

will

give

you

2.Y

ouha

veto

spec

ify

one

ofth

eop

eran

dsas

aflo

atto

gett

rue

divi

sion

,e.g

.5/2.

or5./2

(the

dot

spec

ifies

you

wan

tto

wor

kw

ithflo

at)t

oha

ve2.

5.Th

isbe

havi

oris

depr

ecat

edan

dw

illdi

sapp

ear

ina

futu

repy

thon

rele

ase

assh

own

from

the

from

__-

future__import

.

>>>

5/2

2 >>>5/2.

2.5

>>>5./2

2.5

>>>

from

__future__

import

division

>>>

5/2

2.5

>>>

5//2

2

8St

ring

s

8.1

Stri

ngm

anip

ulat

ion

8.1.

1St

ring

oper

atio

ns

Equ

ality

Two

stri

ngs

are

equa

lif

and

only

ifth

eyha

veex

actly

the

sam

eco

nten

ts,

mea

ning

that

they

are

both

the

sam

ele

ngth

and

each

char

acte

rhas

aon

e-to

-one

posi

tiona

lcor

resp

onde

nce.

Man

yot

herl

angu

ages

test

strin

gson

lyfo

ride

ntity

;

53

that

is,t

hey

only

test

whe

ther

two

stri

ngs

occu

pyth

esa

me

spac

ein

mem

ory.

Thi

sla

ttero

pera

tion

ispo

ssib

lein

Pyth

onus

ing

the

oper

atoris

.

Exa

mpl

e:

>>>

a=

'hello';

b=

'hello'#

Assign

'hello'

to

aand

b.

>>>

printa

==

b#

True

True

>>>

printa

==

'hello'

#True

>>>

printa

==

"hello"

#(choice

of

delimiter

is

unimportant)

True

>>>

printa

==

'hello

'#

(extra

space)

False

>>>

printa

==

'Hello'

#(wrong

case)

False

>>>

ais

a#

True

True

>>>

ais

b#

True,

because

python

caches

small

strings,

thus

stores

both

strings

in

the

same

location

True

>>>

ais

'hello'

#In

this

case

'hello'

uses

another

cache

then

variables

False

>>>

'hello'

is

'hello'

#But

all

'hello's

use

the

same

cache

True

>>>

a*2

is

a*2

#No

caching

if

operations

are

applied

False

Num

eric

al

Ther

ear

etw

oqu

asi-n

umer

ical

oper

atio

nsw

hich

can

bedo

neon

strin

gs--

addi

-tio

nan

dm

ultip

licat

ion.

Strin

gad

ditio

nis

just

anot

hern

ame

forc

onca

tena

tion.

Stri

ngm

ultip

licat

ion

isre

petit

ive

addi

tion,

orco

ncat

enat

ion.

So:

>>>

c=

'a'

>>>

c+

'b'

'ab'

>>>

c*5

'aaaaa'

Con

tain

men

t

Ther

eis

asi

mpl

eop

erat

or'in

'tha

tret

urns

True

ifth

efir

stop

eran

dis

cont

aine

din

the

seco

nd.T

his

also

wor

kson

subs

trin

gs

>>>

x=

'hello'

>>>

y=

'ell'

>>>

xin

yFalse

>>>

yin

xTrue

Not

eth

at'p

rint

xin

y'w

ould

have

also

retu

rned

the

sam

eva

lue.

Inde

xing

and

Slic

ing

Muc

hlik

ear

rays

inot

herl

angu

ages

,the

indi

vidu

alch

arac

ters

ina

strin

gca

nbe

acce

ssed

byan

inte

gerr

epre

sent

ing

itspo

sitio

nin

the

strin

g.Th

efir

stch

arac

ter

inst

ring

sw

ould

bes[

0]an

dth

ent

hch

arac

terw

ould

beat

s[n-

1].

>>>

s=

"Xanadu"

>>>

s[1]

'a'

Unl

ike

arra

ysin

othe

rlan

guag

es,P

ytho

nal

soin

dexe

sth

ear

rays

back

war

ds,

usin

gne

gativ

enu

mbe

rs.

The

last

char

acte

rha

sin

dex

-1,t

hese

cond

tola

stch

arac

terh

asin

dex

-2,a

ndso

on.

>>>

s[-4]

'n'

We

can

also

use

"slic

es"

toac

cess

asu

bstr

ing

ofs.

s[a:

b]w

illgi

veus

ast

ring

star

ting

with

s[a]

and

endi

ngw

iths[

b-1]

.

>>>

s[1:4]

'ana'

Non

eof

thes

ear

eas

sign

able

.

>>>

prints

>>>

s[0]

='J'

Traceback

(most

recent

call

last):

File

"<stdin>",

line

1,

in

?TypeError:

object

does

not

support

item

assignment

>>>

s[1:3]

="up"

Traceback

(most

recent

call

last):

File

"<stdin>",

line

1,

in

?TypeError:

object

does

not

support

sliceassignment

>>>

prints

Out

puts

(ass

umin

gth

eer

rors

wer

esu

ppre

ssed

):

Xanadu

Xanadu

Ano

ther

feat

ure

ofsl

ices

isth

atif

the

begi

nnin

gor

end

isle

ftem

pty,

itw

illde

faul

tto

the

first

orla

stin

dex,

depe

ndin

gon

cont

ext:

>>>

s[2:]

'nadu'

>>>

s[:3]

'Xan'

>>>

s[:]

'Xanadu'

You

can

also

use

nega

tive

num

bers

insl

ices

:

>>>

prints[-2:]

'du'

Toun

ders

tand

slic

es,i

t'sea

sies

tnot

toco

untt

heel

emen

tsth

emse

lves

.Iti

sa

bitl

ike

coun

ting

noto

nyo

urfin

gers

,but

inth

esp

aces

betw

een

them

.The

list

isin

dexe

dlik

eth

is:

Element:

12

34

Index:

01

23

-4

-3

-2

-1

So,w

hen

we

ask

fort

he[1

:3]s

lice,

that

mea

nsw

est

arta

tind

ex1,

and

end

atin

dex

3,an

dta

keev

eryt

hing

inbe

twee

nth

em.I

fyou

are

used

toin

dexe

sin

Cor

Java

,thi

sca

nbe

abi

tdis

conc

ertin

gun

tilyo

uge

tuse

dto

it.

8.1.

2St

ring

cons

tant

s

Stri

ngco

nsta

nts

can

befo

und

inth

est

anda

rdst

ring

mod

ule.

Eith

ersi

ngle

ordo

uble

quot

esm

aybe

used

tode

limit

stri

ngco

nsta

nts.

8.1.

3St

ring

met

hods

The

rear

ea

num

bero

fmet

hods

orbu

ilt-i

nst

ring

func

tions

:

•ca

pita

lize

•ce

nter

•co

unt

•de

code

•en

code

•en

dsw

ith•

expa

ndta

bs•

find

•in

dex

•is

alnu

m•

isal

pha

•is

digi

t•

islo

wer

•is

spac

e•

istit

le•

isup

per

•jo

in•

ljust

•lo

wer

•ls

trip

•re

plac

e•

rfind

•ri

ndex

•rj

ust

•rs

trip

•sp

lit•

split

lines

•st

arts

with

•st

rip

•sw

apca

se•

title

•tr

ansl

ate

•up

per

•zfi

ll

Onl

yem

phas

ized

item

sw

illbe

cove

red.

is*

isal

num

(),i

salp

ha()

,isd

igit(

),is

low

er()

,isu

pper

(),i

sspa

ce()

,and

istit

le()

fitin

toth

isca

tego

ry.

The

leng

thof

the

stri

ngob

ject

bein

gco

mpa

red

mus

tbe

atle

ast1

,or

the

is*

met

hods

will

retu

rnFa

lse.

Inot

herw

ords

,ast

ring

obje

ctof

len(

stri

ng)=

=0,

isco

nsid

ered

"em

pty"

,orF

alse

.

•is

alnu

mre

turn

sTr

ueif

the

stri

ngis

entir

ely

com

pose

dof

alph

abet

ican

d/or

num

eric

char

acte

rs(i

.e.n

opu

nctu

atio

n).

•is

alph

aan

dis

digi

tw

ork

sim

ilarl

yfo

ral

phab

etic

char

acte

rsor

num

eric

char

acte

rson

ly.

•is

spac

ere

turn

sTr

ueif

the

stri

ngis

com

pose

den

tirel

yof

whi

tesp

ace.

•is

low

er,i

supp

er,a

ndis

title

retu

rnTr

ueif

the

stri

ngis

inlo

wer

case

,upp

er-

case

,or

title

case

resp

ectiv

ely.

Unc

ased

char

acte

rsar

e"a

llow

ed",

such

asdi

gits

,but

ther

em

ustb

eat

leas

tone

case

dch

arac

teri

nth

est

ring

obje

ctin

orde

rto

retu

rnTr

ue.T

itlec

ase

mea

nsth

efir

stca

sed

char

acte

rofe

ach

wor

dis

uppe

rcas

e,an

dan

yim

med

iate

lyfo

llow

ing

case

dch

arac

ters

are

low

erca

se.

Cur

ious

ly,'

Y2K

'.ist

itle(

)ret

urns

True

.Tha

tis

beca

use

uppe

rcas

ech

arac

ters

can

only

follo

wun

case

dch

arac

ters

.Lik

ewis

e,lo

wer

case

char

acte

rsca

non

lyfo

llow

uppe

rcas

eor

low

erca

sech

arac

ters

.Hin

t:w

hite

spac

eis

unca

sed.

Exa

mpl

e:

>>>

'2YK'.istitle()

False

>>>

'Y2K'.istitle()

True

>>>

'2Y

K'.istitle()

True

title

,upp

er,l

ower

,sw

apca

se,c

apita

lize

Ret

urns

the

stri

ngco

nver

ted

totit

leca

se,u

pper

case

,low

erca

se,i

nver

tsca

se,

orca

pita

lizes

,res

pect

ivel

y.

The

title

met

hod

capi

taliz

esth

efir

stle

tter

ofea

chw

ord

inth

est

ring

(and

mak

esth

ere

stlo

wer

case

).W

ords

are

iden

tified

assu

bstr

ings

ofal

phab

etic

char

acte

rsth

atar

ese

para

ted

byno

n-al

phab

etic

char

acte

rs,s

uch

asdi

gits

,or

whi

tesp

ace.

Thi

sca

nle

adto

som

eun

expe

cted

beha

vior

.Fo

rex

ampl

e,th

est

ring

"x1x

"w

illbe

conv

erte

dto

"X1X

"in

stea

dof

"X1x

".

The

swap

case

met

hod

mak

esal

lupp

erca

sele

tters

low

erca

sean

dvi

ceve

rsa.

The

capi

taliz

em

etho

dis

like

title

exce

ptth

atit

cons

ider

sth

een

tire

stri

ngto

bea

wor

d.(i

.e.i

tmak

esth

efir

stch

arac

teru

pper

case

and

the

rest

low

erca

se)

Exa

mpl

e:

>>>

s=

'Hello,

wOrLD'

>>>

s'Hello,

wOrLD'

>>>

s.title()

'Hello,

World'

>>>

s.swapcase()

'hELLO,

WoRld'

>>>

s.upper()

'HELLO,

WORLD'

>>>

s.lower()

'hello,

world'

>>>

s.capitalize()

'Hello,

world'

coun

t

Ret

urns

the

num

bero

fthe

spec

ified

subs

trin

gsin

the

stri

ng.i

.e.

>>>

s=

'Hello,

world'

>>>

s.count('o')

#print

the

number

of

'o's

in

'Hello,

World'

(2)

2 Hin

t:.c

ount

()is

case

-sen

sitiv

e,so

this

exam

ple

will

only

coun

tthe

num

bero

flo

wer

case

lette

r'o'

s.Fo

rexa

mpl

e,if

you

ran:

>>>

s=

'HELLO,

WORLD'

>>>

s.count('o')

#print

the

number

of

lowercase

'o's

in

'HELLO,

WORLD'

(0)

0

stri

p,rs

trip

,lst

rip

Ret

urns

aco

pyof

the

stri

ngw

ithth

ele

adin

g(l

stri

p)an

dtr

ailin

g(r

stri

p)w

hite

spac

ere

mov

ed.s

trip

rem

oves

both

.

>>>

s=

'\t

Hello,

world\n\t

'>>>

printsHello,

world

>>>

prints.strip()

Hello,

world

>>>

prints.lstrip()

Hello,

world

#ends

here

>>>

prints.rstrip()

Hello,

world

Not

eth

ele

adin

gan

dtr

ailin

gta

bsan

dne

wlin

es.

Stri

pm

etho

dsca

nal

sobe

used

tore

mov

eot

hert

ypes

ofch

arac

ters

.

import

string

s=

'www.wikibooks.org'

print

sprint

s.strip('w')

#Removes

all

w's

from

outside

print

s.strip(string.lowercase)

#Removes

all

lowercase

letters

from

outside

print

s.strip(string.printable)

#Removes

all

printable

characters

Out

puts

:

www.wikibooks.org

.wikibooks.org

.wikibooks.

Not

eth

atst

ring

.low

erca

sean

dst

ring

.pri

ntab

lere

quir

ean

impo

rtst

ring

stat

e-m

ent

ljust

,rju

st,c

ente

r

left

,rig

htor

cent

erju

stifi

esa

stri

ngin

toa

give

nfie

ldsi

ze(t

here

stis

padd

edw

ithsp

aces

).

>>>

s=

'foo'

>>>

s'foo'

>>>

s.ljust(7)

'foo

'>>>

s.rjust(7)

'foo'

>>>

s.center(7)

'foo

'

join

Join

sto

geth

erth

egi

ven

sequ

ence

with

the

stri

ngas

sepa

rato

r:

>>>

seq

=['1',

'2',

'3',

'4',

'5']

>>>

''.join(seq)

'1

23

45'

>>>

'+'.join(seq)

'1+2+3+4+5'

map

may

behe

lpfu

lher

e:(i

tcon

vert

snu

mbe

rsin

seq

into

stri

ngs)

>>>

seq

=[1,2,3,4,5]

>>>

''.join(map(str,

seq))

'1

23

45'

now

arbi

trar

yob

ject

sm

aybe

inse

qin

stea

dof

just

stri

ngs.

find,

inde

x,rfi

nd,r

inde

x

The

find

and

inde

xm

etho

dsre

turn

the

inde

xof

the

first

foun

doc

curr

ence

ofth

egi

ven

subs

eque

nce.

Ifit

isno

tfou

nd,fi

ndre

turn

s-1

buti

ndex

rais

esa

Val

ueE

rror

.rfi

ndan

dri

ndex

are

the

sam

eas

find

and

inde

xex

cept

that

they

sear

chth

roug

hth

est

ring

from

righ

tto

left

(i.e

.the

yfin

dth

ela

stoc

curr

ence

)

>>>

s=

'Hello,

world'

>>>

s.find('l')

2 >>>

s[s.index('l'):]

'llo,

world'

>>>

s.rfind('l')

10>>>

s[:s.rindex('l')]

'Hello,

wor'

>>>

s[s.index('l'):s.rindex('l')]

'llo,

wor'

Bec

ause

Pyth

onst

ring

sac

cept

nega

tive

subs

crip

ts,i

ndex

ispr

obab

lybe

tter

used

insi

tuat

ions

like

the

one

show

nbe

caus

eus

ing

find

inst

ead

wou

ldyi

eld

anun

inte

nded

valu

e.

repl

ace

Rep

lace

wor

ksju

stlik

eit

soun

ds.

Itre

turn

sa

copy

ofth

est

ring

with

all

occu

rren

ces

ofth

efir

stpa

ram

eter

repl

aced

with

the

seco

ndpa

ram

eter

.

>>>

'Hello,

world'.replace('o',

'X')

'HellX,

wXrld'

Or,

usin

gva

riab

leas

sign

men

t:

string

='Hello,

world'

newString

=string.replace('o',

'X')

print

string

print

newString

Out

puts

:

Hello,

world

HellX,

wXrld

Not

ice,

the

orig

inal

vari

able

(string

)re

mai

nsun

chan

ged

afte

rth

eca

llto

replace

.

expa

ndta

bs

Rep

lace

sta

bsw

ithth

eap

prop

riate

num

bero

fspa

ces

(def

ault

num

bero

fspa

ces

pert

ab=

8;th

isca

nbe

chan

ged

bypa

ssin

gth

eta

bsi

zeas

anar

gum

ent)

.

s=

'abcdefg\tabc\ta'

print

sprint

len(s)

t=

s.expandtabs()

print

tprint

len(t)

Out

puts

:

abcdefg

abc

a13

abcdefg

abc

a17

Not

ice

how

(alth

ough

thes

ebo

thlo

okth

esa

me)

the

seco

ndst

ring

(t)

has

adi

ffer

entl

engt

hbe

caus

eea

chta

bis

repr

esen

ted

bysp

aces

nott

abch

arac

ters

.

Tous

ea

tab

size

of4

inst

ead

of8:

v=

s.expandtabs(4)

print

vprint

len(v)

Out

puts

:

abcdefg

abc

a13

Plea

seno

teea

chta

bis

not

alw

ays

coun

ted

asei

ght

spac

es.

Rat

her

ata

b"p

ushe

s"th

eco

untt

oth

ene

xtm

ultip

leof

eigh

t.Fo

rexa

mpl

e:

s=

'\t\t'

print

s.expandtabs().replace('

',

'*')

print

len(s.expandtabs())

Out

put:

****************

16

s=

'abc\tabc\tabc'

print

s.expandtabs().replace('

',

'*')

print

len(s.expandtabs())

Out

puts

:

abc*****abc*****abc

19

split

,spl

itlin

es

The

split

met

hod

retu

rns

alis

toft

hew

ords

inth

est

ring.

Itca

nta

kea

sepa

rato

rar

gum

entt

ous

ein

stea

dof

whi

tesp

ace.

>>>

s=

'Hello,

world'

>>>

s.split()

['Hello,',

'world']

>>>

s.split('l')

['He',

'',

'o,

wor',

'd']

Not

eth

atin

neith

erca

seis

the

sepa

rato

rinc

lude

din

the

split

strin

gs,b

utem

pty

stri

ngs

are

allo

wed

.

The

split

lines

met

hod

brea

ksa

mul

tilin

est

ring

into

man

ysi

ngle

line

stri

ngs.

Itis

anal

ogou

sto

split

('\n'

)(b

utac

cept

s'\r

'and

'\r\n

'as

delim

iters

asw

ell)

exce

ptth

atif

the

strin

gen

dsin

ane

wlin

ech

arac

ter,

split

lines

igno

res

that

final

char

acte

r(se

eex

ampl

e).

>>>

s=

"""

...

One

line

...

Two

lines

...

Red

lines

...

Blue

lines

...

Green

lines

...

"""

>>>

s.split('\n')

['',

'One

line',

'Two

lines',

'Red

lines',

'Blue

lines',

'Green

lines',

'']

>>>

s.splitlines()

['',

'One

line',

'Two

lines',

'Red

lines',

'Blue

lines',

'Green

lines']

9L

ists

9.1

Abo

utlis

tsin

Pyth

on

Alis

tin

Pyth

onis

anor

dere

dgr

oup

ofite

ms

(ore

lem

ents

).It

isa

very

gene

ral

stru

ctur

e,an

dlis

tele

men

tsdo

n'th

ave

tobe

ofth

esa

me

type

.For

inst

ance

,you

coul

dpu

tnum

bers

,let

ters

,and

stri

ngs

allo

nth

esa

me

list.

Ifyo

uar

eus

ing

am

oder

nve

rsio

nof

Pyth

on(a

ndyo

ush

ould

be),

ther

eis

acl

ass

calle

d'li

st'.

Ifyo

uw

ish,

you

can

mak

eyo

urow

nsu

bcla

ssof

it,an

dde

term

ine

listb

ehav

iour

whi

chis

diff

eren

ttha

nth

ede

faul

tsta

ndar

d.B

utfir

st,

you

shou

ldbe

fam

iliar

with

the

curr

entb

ehav

iour

oflis

ts.

79

9.1.

1L

istn

otat

ion

The

rear

etw

odi

ffer

entw

ays

tom

ake

alis

tin

Pyth

on.

The

first

isth

roug

has

sign

men

t("s

tatic

ally

"),t

hese

cond

isus

ing

listc

ompr

ehen

sion

s("a

ctiv

ely"

).

Tom

ake

ast

atic

listo

fite

ms,

writ

eth

embe

twee

nsq

uare

brac

kets

.For

exam

ple:

[1,2,3,"This

is

alist",'c',Donkey("kong")

]

Aco

uple

ofth

ings

tolo

okat

.

1.T

here

are

diff

eren

tdat

aty

pes

here

.Lis

tsin

Pyth

onm

ayco

ntai

nm

ore

than

one

data

type

.2.

Obj

ects

can

becr

eate

d'o

nth

efly

'and

adde

dto

lists

.The

last

item

isa

new

kind

ofD

onke

y.

Wri

ting

lists

this

way

isve

ryqu

ick

(and

obvi

ous)

.How

ever

,itd

oes

nott

ake

into

acco

untt

hecu

rren

tsta

teof

anyt

hing

else

.The

othe

rway

tom

ake

alis

tis

tofo

rmit

usin

glis

tcom

preh

ensi

on.T

hatm

eans

you

actu

ally

desc

ribe

the

proc

ess.

Todo

that

,the

listi

sbr

oken

into

two

piec

es.T

hefir

stis

api

ctur

eof

wha

teac

hel

emen

twill

look

like,

and

the

seco

ndis

wha

tyou

doto

geti

t.

Fori

nsta

nce,

lets

say

we

have

alis

tofw

ords

:

listOfWords

=["this","is","a","list","of","words"]

Lis

tcom

preh

ensi

ons

-->

see

also

Tips

and

Tric

ks1

We

will

take

the

first

lette

rof

each

wor

dan

dm

ake

alis

tou

tof

it(u

sing

so-c

alle

dlis

tcom

preh

ensi

on).

>>>

listOfWords

=["this","is","a","list","of","words"]

>>>

items

=[

word[0]

forword

in

listOfWords

]

1http://en.wikibooks.org/wiki/Python%20Programming%2FTips_

and_Tricks%23List_comprehension_and_generators

>>>

printitems

['t',

'i',

'a',

'l',

'o',

'w']

Lis

tcom

preh

ensi

onal

low

syo

uto

use

mor

eth

anon

efo

rst

atem

ent.

Itw

illev

alua

teth

eite

ms

inal

lof

the

obje

cts

sequ

entia

llyan

dw

illlo

opov

erth

esh

orte

robj

ects

ifon

eob

ject

islo

nger

than

the

rest

.

>>>

item

=[x+y

forx

in

'flower'

fory

in

'pot']

>>>

printitem

['fp',

'fo',

'ft',

'lp',

'lo',

'lt',

'op',

'oo',

'ot',

'wp',

'wo',

'wt',

'ep',

'eo',

'et',

'rp',

'ro',

'rt']

Lis

tcom

preh

ensi

onal

soal

low

syo

uto

use

anif

stat

emen

t,to

only

incl

ude

mem

bers

into

the

listt

hatf

ulfil

lace

rtai

nco

nditi

on.W

eca

nth

usex

clud

eal

lca

ses

whe

rex

iseq

ualt

ow

and

yis

equa

lto

o;or

we

can

only

excl

ude

the

case

whe

rex

iseq

ualt

ow

and

yis

equa

lto

o(a

ndth

usre

mov

ing

the

'wo'

from

the

list)

.

>>>

print[x+yfor

xin

'flower'

fory

in

'pot']

['fp',

'fo',

'ft',

'lp',

'lo',

'lt',

'op',

'oo',

'ot',

'wp',

'wo',

'wt',

'ep',

'eo',

'et',

'rp',

'ro',

'rt']

>>>

print[x+yfor

xin

'flower'

fory

in

'pot'

ifx

!=

'w'

and

y!=

'o'

]['fp',

'ft',

'lp',

'lt',

'op',

'ot',

'ep',

'et',

'rp',

'rt']

>>>

print[x+yfor

xin

'flower'

fory

in

'pot'

ifx

!=

'w'

or

y!=

'o'

]['fp',

'fo',

'ft',

'lp',

'lo',

'lt',

'op',

'oo',

'ot',

'wp',

'wt',

'ep',

'eo',

'et',

'rp',

'ro',

'rt']

Pyth

on's

listc

ompr

ehen

sion

does

notd

efine

asc

ope.

Any

vari

able

sth

atar

ebo

und

inan

eval

uatio

nre

mai

nbo

und

tow

hate

vert

hey

wer

ela

stbo

und

tow

hen

the

eval

uatio

nw

asco

mpl

eted

:

>>>

printx,

yr

t

Thi

sis

exac

tlyth

esa

me

asif

the

com

preh

ensi

onha

dbe

enex

pand

edin

toan

expl

icitl

y-ne

sted

grou

pof

one

orm

ore

'for'

stat

emen

tsan

d0

orm

ore

'if'

stat

emen

ts.

Lis

tcre

atio

nsh

ortc

uts

Pyth

onpr

ovid

esa

shor

tcut

toin

itial

ize

alis

tto

apa

rtic

ular

size

and

with

anin

itial

valu

efo

reac

hel

emen

t:

>>>

zeros=[0]*5

>>>

printzeros

[0,

0,

0,

0,

0]

Thi

sw

orks

fora

nyda

taty

pe:

>>>

foos=['foo']*8

>>>

printfoos

['foo',

'foo',

'foo',

'foo',

'foo',

'foo',

'foo',

'foo']

with

aca

veat

.Whe

nbu

ildin

ga

new

listb

ym

ultip

lyin

g,Py

thon

copi

esea

chite

mby

refe

renc

e.T

his

pose

sa

prob

lem

form

utab

leite

ms,

fori

nsta

nce

ina

mul

tidim

ensi

onal

arra

yw

here

each

elem

enti

sits

elfa

list.

You'

dgu

ess

that

the

easy

way

toge

nera

tea

two

dim

ensi

onal

arra

yw

ould

be:

listoflists=[

[0]*4

]*5

and

this

wor

ks,b

utpr

obab

lydo

esn'

tdo

wha

tyou

expe

ct:

>>>

listoflists=[

[0]*4

]*5

>>>

printlistoflists

[[0,

0,

0,

0],

[0,

0,

0,

0],

[0,

0,

0,

0],

[0,

0,

0,

0],

[0,

0,

0,

0]]

>>>

listoflists[0][2]=1

>>>

printlistoflists

[[0,

0,

1,

0],

[0,

0,

1,

0],

[0,

0,

1,

0],

[0,

0,

1,

0],

[0,

0,

1,

0]]

Wha

t'sha

ppen

ing

here

isth

atPy

thon

isus

ing

the

sam

ere

fere

nce

toth

ein

ner

lista

sth

eel

emen

tsof

the

oute

rlis

t.A

noth

erw

ayof

look

ing

atth

isis

sue

isto

exam

ine

how

Pyth

onse

esth

eab

ove

defin

ition

:

>>>

innerlist=[0]*4

>>>

listoflists=[innerlist]*5

>>>

printlistoflists

[[0,

0,

0,

0],

[0,

0,

0,

0],

[0,

0,

0,

0],

[0,

0,

0,

0],

[0,

0,

0,

0]]

>>>

innerlist[2]=1

>>>

printlistoflists

[[0,

0,

1,

0],

[0,

0,

1,

0],

[0,

0,

1,

0],

[0,

0,

1,

0],

[0,

0,

1,

0]]

Ass

umin

gth

eab

ove

effe

ctis

notw

haty

ouin

tend

,one

way

arou

ndth

isis

sue

isto

use

listc

ompr

ehen

sion

s:

>>>

listoflists=[[0]*4fori

in

range(5)]

>>>

printlistoflists

[[0,

0,

0,

0],

[0,

0,

0,

0],

[0,

0,

0,

0],

[0,

0,

0,

0],

[0,

0,

0,

0]]

>>>

listoflists[0][2]=1

>>>

printlistoflists

[[0,

0,

1,

0],

[0,

0,

0,

0],

[0,

0,

0,

0],

[0,

0,

0,

0],

[0,

0,

0,

0]]

9.1.

2O

pera

tions

onlis

ts

Lis

tAtt

ribu

tes

Tofin

dth

ele

ngth

ofa

listu

seth

ebu

iltin

len(

)met

hod.

>>>

len([1,2,3])

3 >>>

a=

[1,2,3,4]

>>>

len(

a)

4 Com

bini

nglis

ts

Lis

tsca

nbe

com

bine

din

seve

ralw

ays.

The

easi

esti

sju

stto

'add

'the

m.F

orin

stan

ce:

>>>

[1,2]

+[3,4]

[1,

2,

3,

4]

Ano

ther

way

toco

mbi

nelis

tsis

with

exte

nd.

Ifyo

une

edto

com

bine

lists

insi

deof

ala

mbd

a,ex

tend

isth

ew

ayto

go.

>>>

a=

[1,2,3]

>>>

b=

[4,5,6]

>>>

a.extend(b)

>>>

printa

[1,

2,

3,

4,

5,

6]

The

othe

rway

toap

pend

ava

lue

toa

listi

sto

use

appe

nd.F

orex

ampl

e:

>>>

p=[1,2]

>>>

p.append([3,4])

>>>

p[1,

2,

[3,

4]]

>>>

#or

>>>

printp

[1,

2,

[3,

4]]

How

ever

,[3,

4]is

anel

emen

toft

helis

t,an

dno

tpar

toft

helis

t.ap

pend

alw

ays

adds

one

elem

ento

nly

toth

een

dof

alis

t.So

ifth

ein

tent

ion

was

toco

ncat

enat

etw

olis

ts,a

lway

sus

eex

tend

.

Get

ting

piec

esof

lists

(slic

es)

Con

tinuo

ussl

ices

Lik

est

ring

s2 ,lis

tsca

nbe

inde

xed

and

slic

ed.

>>>

list

=[2,

4,

"usurp",

9.0,"n"]

>>>

list[2]

'usurp'

>>>

list[3:]

[9.0,

'n']

2C

hapt

er8

onpa

ge53

Muc

hlik

eth

esl

ice

ofa

strin

gis

asu

bstri

ng,t

hesl

ice

ofa

listi

sa

list.

How

ever

,lis

tsdi

ffer

from

stri

ngs

inth

atw

eca

nas

sign

new

valu

esto

the

item

sin

alis

t.

>>>

list[1]

=17

>>>

list

[2,

17,

'usurp',

9.0,'n']

We

can

even

assi

gnne

wva

lues

tosl

ices

ofth

elis

ts,w

hich

don'

teve

nha

veto

beth

esa

me

leng

th

>>>

list[1:4]

=["opportunistic",

"elk"]

>>>

list

[2,

'opportunistic',

'elk',

'n']

It's

even

poss

ible

toap

pend

thin

gson

toth

een

dof

lists

byas

sign

ing

toan

empt

ysl

ice:

>>>

list[:0]

=[3.14,2.71]

>>>

list

[3.14,

2.71,

2,

'opportunistic',

'elk',

'n']

You

can

also

com

plet

ely

chan

geco

nten

tsof

alis

t:

>>>

list[:]

=['new',

'list',

'contents']

>>>

list

['new',

'list',

'contents']

On

the

righ

t-ha

ndsi

deof

assi

gnm

ents

tate

men

tcan

bean

yite

rabl

ety

pe:

>>>

list[:2]

=('element',('t',),[])

>>>

list

['element',

('t',),

[],

'contents']

With

slic

ing

you

can

crea

teco

pyof

listb

ecau

sesl

ice

retu

rns

ane

wlis

t:

>>>

original

=[1,

'element',

[]]

>>>

list_copy

=original[:]

>>>

list_copy

[1,

'element',

[]]

>>>

list_copy.append('new

element')

>>>

list_copy

[1,

'element',

[],

'new

element']

>>>

original

[1,

'element',

[]]

butt

his

issh

allo

wco

pyan

dco

ntai

nsre

fere

nces

toel

emen

tsfr

omor

igin

allis

t,so

beca

refu

lwith

mut

able

type

s:

>>>

list_copy[2].append('something')

>>>

original

[1,

'element',

['something']]

Non

-Con

tinuo

ussl

ices

Itis

also

poss

ible

toge

tnon

-con

tinuo

uspa

rts

ofan

arra

y.If

one

wan

ted

toge

tev

ery

n-th

occu

rren

ceof

alis

t,on

ew

ould

use

the

::op

erat

or.

The

synt

axis

a:b:

nw

here

aan

db

are

the

star

tand

end

ofth

esl

ice

tobe

oper

ated

upon

.

>>>

list

=[ifor

iin

range(10)

]>>>

list

[0,

1,

2,

3,

4,

5,

6,

7,

8,

9]

>>>

list[::2]

[0,

2,

4,

6,

8]

>>>

list[1:7:2]

[1,

3,

5]

Com

pari

nglis

ts

Lis

tsca

nbe

com

pare

dfo

requ

ality

.

>>>

[1,2]

==

[1,2]

True

>>>

[1,2]

==

[3,4]

False

Sort

ing

lists

Sort

ing

lists

isea

syw

itha

sort

met

hod.

>>>

list

=[2,

3,

1,

'a',

'b']

>>>

list.sort()

>>>

list

[1,

2,

3,

'a',

'b']

Not

eth

atth

elis

tis

sort

edin

plac

e,an

dth

eso

rt()

met

hod

retu

rns

Non

eto

emph

asiz

eth

issi

deef

fect

.

Ifyo

uus

ePy

thon

2.4

orhi

gher

ther

ear

eso

me

mor

eso

rtpa

ram

eter

s:

sort

(cm

p,ke

y,re

vers

e)

cmp

:met

hod

tobe

used

fors

ortin

gke

y:f

unct

ion

tobe

exec

uted

with

key

ele-

men

t.Li

stis

sorte

dby

retu

rn-v

alue

ofth

efu

nctio

nre

vers

e:s

ort(r

ever

se=T

rue)

orso

rt(r

ever

se=F

alse

)

Pyth

onal

soin

clud

esa

sort

ed()

func

tion.

>>>

list

=[5,

2,

3,

'q',

'p']

>>>

sorted(list)

[2,

3,

5,

'p',

'q']

>>>

list

[5,

2,

3,

'q',

'p']

Not

eth

atun

like

the

sort

()m

etho

d,so

rted

(lis

t)do

esno

tsor

tthe

listi

npl

ace,

buti

nste

adre

turn

sth

eso

rted

list.

The

sorte

d()f

unct

ion,

like

the

sort(

)met

hod

also

acce

pts

the

reve

rse

para

met

er.

9.2

Lis

tmet

hods

9.2.

1ap

pend

(x)

Add

item

xon

toth

een

dof

the

list.

>>>

list

=[1,

2,

3]

>>>

list.append(4)

>>>

list

[1,

2,

3,

4]

See

pop(

i)3

9.2.

2po

p(i)

Rem

ove

the

item

inth

elis

tatt

hein

dex

iand

retu

rnit.

Ifii

sno

tgiv

en,r

emov

eth

eth

ela

stite

min

the

lista

ndre

turn

it.

>>>

list

=[1,

2,

3,

4]

>>>

a=

list.pop(0)

>>>

list

[2,

3,

4]

>>>

a1 >>>

b=

list.pop()

>>>list

[2,

3]

>>>

b4 3

Cha

pter

9.2.

2on

page

96

9.3

oper

ator

s

9.3.

1in

the

oper

ator

'in'i

sus

edfo

rtw

opu

rpos

eset

hert

oite

rate

over

ever

yite

min

alis

tin

afo

rloo

por

toch

eck

ifa

valu

eis

ina

listr

etun

ing

true

orfa

lse.

>>>

list

=[1,

2,

3,

4]

>>>

if3

in

list:

>>>

....

>>>

l=

[0,

1,

2,

3,

4]

>>>

3in

lTrue

>>>

18

in

lFalse

}}

10D

ictio

nari

es

10.1

Abo

utdi

ctio

nari

esin

Pyth

on

Adi

ctio

nary

inpy

thon

isa

colle

ctio

nof

unor

dere

dva

lues

whi

char

eac

cess

edby

key.

10.1

.1D

ictio

nary

nota

tion

Dic

tiona

riesm

aybe

crea

ted

dire

ctly

orco

nver

ted

from

sequ

ence

s.D

ictio

narie

sar

een

clos

edin

curl

ybr

aces

,{}

99

>>>

d=

{'city':'Paris',

'age':38,

(102,1650,1601):'A

matrix

coordinate'}

>>>

seq

=[('city','Paris'),

('age',

38),

((102,1650,1601),'A

matrix

coordinate')]

>>>

d{'city':

'Paris',

'age':

38,

(102,

1650,

1601):

'A

matrix

coordinate'}

>>>

dict(seq)

{'city':

'Paris',

'age':

38,

(102,

1650,

1601):

'A

matrix

coordinate'}

>>>

d==

dict(seq)

True

Als

o,di

ctio

nari

esca

nbe

easi

lycr

eate

dby

zipp

ing

two

sequ

ence

s.

>>>

seq1

=('a','b','c','d')

>>>

seq2

=[1,2,3,4]

>>>

d=

dict(zip(seq1,seq2))

>>>

d{'a':

1,

'c':

3,

'b':

2,

'd':

4}

10.1

.2O

pera

tions

onD

ictio

nari

es

The

oper

atio

nson

dict

iona

ries

are

som

ewha

tuni

que.

Slic

ing

isno

tsup

port

ed,

sinc

eth

eite

ms

have

noin

trin

sic

orde

r.

>>>

d=

{'a':1,'b':2,

'cat':'Fluffers'}

>>>

d.keys()

['a',

'b',

'cat']

>>>

d.values()

[1,

2,

'Fluffers']

>>>

d['a']

1 >>>

d['cat']

='Mr.

Whiskers'

>>>

d['cat']

'Mr.

Whiskers'

>>>

'cat'

in

dTrue

>>>

'dog'

in

dFalse

10.1

.3C

ombi

ning

two

Dic

tiona

ries

You

can

com

bine

two

dict

iona

ries

byus

ing

the

upda

tem

etho

dof

the

prim

ary

dict

iona

ry.N

ote

that

the

upda

tem

etho

dw

illm

erge

exis

ting

elem

ents

ifth

eyco

nflic

t.

>>>

d=

{'apples':

1,

'oranges':

3,

'pears':

2}

>>>

ud

={'pears':

4,

'grapes':

5,

'lemons':

6}

>>>

d.update(ud)

>>>

d{'grapes':

5,

'pears':

4,

'lemons':

6,

'apples':

1,

'oranges':

3}

>>>

10.1

.4D

elet

ing

from

dict

iona

ry

del

dictionaryName[membername]

11Se

ts

Pyth

onal

soha

san

impl

emen

tatio

nof

the

mat

hem

atic

alse

t1 .Unl

ike

sequ

ence

obje

cts

such

aslis

tsan

dtu

ples

,in

whi

chea

chel

emen

tis

inde

xed,

ase

tis

anun

orde

red

colle

ctio

nof

obje

cts.

Sets

also

cann

otha

vedu

plic

ate

mem

bers

-agi

ven

obje

ctap

pear

sin

ase

t0or

1tim

es.F

orm

ore

info

rmat

ion

onse

ts,s

eeth

eSe

tThe

ory2

wik

iboo

k.Se

tsal

sore

quir

eth

atal

lmem

bers

ofth

ese

tbe

hash

able

.Any

obje

ctth

atca

nbe

used

asa

dict

iona

ryke

yca

nbe

ase

tmem

ber.

1http://en.wikipedia.org/wiki/set%20

2http://en.wikibooks.org/wiki/Set%20Theory

103

Inte

gers

,floa

ting

poin

tnum

bers

,tup

les,

and

stri

ngs

are

hash

able

;dic

tiona

ries

,lis

ts,a

ndot

hers

ets

(exc

eptf

roze

nset

s3 )are

not.

11.0

.5C

onst

ruct

ing

Sets

One

way

toco

nstr

uct

sets

isby

pass

ing

any

sequ

entia

lob

ject

toth

e"s

et"

cons

truc

tor.

>>>

set([0,

1,

2,

3])

set([0,

1,

2,

3])

>>>

set("obtuse")

set(['b',

'e',

'o',

's',

'u',

't'])

We

can

also

add

elem

ents

tose

tson

eby

one,

usin

gth

e"a

dd"

func

tion.

>>>

s=

set([12,

26,

54])

>>>

s.add(32)

3C

hapt

er11

.0.1

1on

page

115

>>>

sset([32,

26,

12,

54])

Not

eth

atsi

nce

ase

tdoe

sno

tcon

tain

dupl

icat

eel

emen

ts,i

fw

ead

don

eof

the

mem

bers

ofs

tos

agai

n,th

ead

dfu

nctio

nw

illha

veno

effe

ct.T

his

sam

ebe

havi

oroc

curs

inth

e"u

pdat

e"fu

nctio

n,w

hich

adds

agr

oup

ofel

emen

tsto

ase

t.

>>>

s.update([26,

12,

9,

14])

>>>

sset([32,

9,

12,

14,

54,

26])

Not

eth

atyo

uca

ngi

vean

yty

peof

sequ

entia

lstr

uctu

re,o

reve

nan

othe

rset

,to

the

upda

tefu

nctio

n,re

gard

less

ofw

hats

truc

ture

was

used

toin

itial

ize

the

set.

The

setf

unct

ion

also

prov

ides

aco

pyco

nstru

ctor

.How

ever

,rem

embe

rtha

tthe

copy

cons

truc

torw

illco

pyth

ese

t,bu

tnot

the

indi

vidu

alel

emen

ts.

>>>

s2

=s.copy()

>>>

s2

set([32,

9,

12,

14,

54,

26])

11.0

.6M

embe

rshi

pTe

stin

g

We

can

chec

kif

anob

ject

isin

the

setu

sing

the

sam

e"i

n"op

erat

oras

with

sequ

entia

ldat

aty

pes.

>>>

32

in

sTrue

>>>

6in

sFalse

>>>

6not

in

sTrue

We

can

also

test

the

mem

bers

hip

ofen

tire

sets

.Giv

entw

ose

tsS 1

and

S 2,w

ech

eck

ifS 1

isa

subs

et4

ora

supe

rset

ofS 2

.

4http://en.wikipedia.org/wiki/Subset

>>>

s.issubset(set([32,

8,

9,

12,

14,

-4,

54,

26,

19]))

True

>>>

s.issuperset(set([9,

12]))

True

Not

eth

at"i

ssub

set"

and

"iss

uper

set"

can

also

acce

ptse

quen

tiald

ata

type

sas

argu

men

ts

>>>

s.issuperset([32,

9])

True

Not

eth

atth

e<=

and

>=op

erat

ors

also

expr

ess

the

issu

bset

and

issu

pers

etfu

nctio

nsre

spec

tivel

y.

>>>

set([4,

5,

7])

<=

set([4,

5,

7,

9])

True

>>>

set([9,

12,

15])

>=

set([9,

12])

True

Lik

elis

ts,t

uple

s,an

dst

ring

,we

can

use

the

"len

"fu

nctio

nto

find

the

num

ber

ofite

ms

ina

set.

11.0

.7R

emov

ing

Item

s

Ther

ear

eth

ree

func

tions

whi

chre

mov

ein

divi

dual

item

sfr

oma

set,

calle

dpo

p,re

mov

e,an

ddi

scar

d.Th

efir

st,p

op,s

impl

yre

mov

esan

item

from

the

set.

Not

eth

atth

ere

isno

defin

edbe

havi

oras

tow

hich

elem

enti

tcho

oses

tore

mov

e.

>>>

s=

set([1,2,3,4,5,6])

>>>

s.pop()

1 >>>

sset([2,3,4,5,6])

We

also

have

the

"rem

ove"

func

tion

tore

mov

ea

spec

ified

elem

ent.

>>>

s.remove(3)

>>>

sset([2,4,5,6])

How

ever

,rem

ovin

ga

item

whi

chis

n'ti

nth

ese

tcau

ses

aner

ror.

>>>

s.remove(9)

Traceback

(most

recent

call

last):

File

"<stdin>",

line

1,

in

?KeyError:

9

Ifyo

uw

ish

toav

oid

this

erro

r,us

e"d

isca

rd."

Itha

sth

esa

me

func

tiona

lity

asre

mov

e,bu

twill

sim

ply

dono

thin

gif

the

elem

enti

sn't

inth

ese

t

We

also

have

anot

hero

pera

tion

forr

emov

ing

elem

ents

from

ase

t,cl

ear,

whi

chsi

mpl

yre

mov

esal

lele

men

tsfr

omth

ese

t.

>>>

s.clear()

>>>

sset([])

11.0

.8It

erat

ion

Ove

rSe

ts

We

can

also

have

alo

opm

ove

over

each

ofth

eite

ms

ina

set.

How

ever

,sin

cese

tsar

eun

orde

red,

itis

unde

fined

whi

chor

dert

heite

ratio

nw

illfo

llow

.

>>>

s=

set("blerg")

>>>

forn

in

s:

...

printn,

...

rb

el

g

11.0

.9Se

tOpe

ratio

ns

Pyth

onal

low

sus

tope

rfor

mal

lth

est

anda

rdm

athe

mat

ical

set

oper

atio

ns,

usin

gm

embe

rsof

set.

Not

eth

atea

chof

thes

ese

tope

ratio

nsha

sse

vera

lfor

ms.

One

ofth

ese

form

s,s1

.func

tion(

s2)

will

retu

rnan

othe

rse

twhi

chis

crea

ted

by"f

unct

ion"

appl

ied

toS 1

and

S 2.

The

othe

rfo

rm,s

1.fu

nctio

n_up

date

(s2)

,w

illch

ange

S 1to

beth

ese

tcre

ated

by"f

unct

ion"

ofS 1

and

S 2.F

inal

ly,s

ome

func

tions

have

equi

vale

ntsp

ecia

lope

rato

rs.F

orex

ampl

e,s1

&s2

iseq

uiva

lent

tos1

.inte

rsec

tion(

s2)

Uni

on

The

unio

n5is

the

mer

gero

ftw

ose

ts.A

nyel

emen

tin

S 1or

S 2w

illap

pear

inth

eiru

nion

.

>>>

s1

=set([4,

6,

9])

>>>

s2

=set([1,

6,

8])

>>>

s1.union(s2)

set([1,

4,

6,

8,

9])

>>>

s1

|s2

set([1,

4,

6,

8,

9])

Not

eth

atun

ion'

sup

date

func

tion

issi

mpl

y"u

pdat

e"ab

ove6 .

5http://en.wikipedia.org/wiki/union_%28set_theory%29

6C

hapt

er11

.0.5

onpa

ge10

4

Inte

rsec

tion

Any

elem

entw

hich

isin

both

S 1an

dS 2

will

appe

arin

thei

rint

erse

ctio

n7 .

>>>

s1

=set([4,

6,

9])

>>>

s2

=set([1,

6,

8])

>>>

s1.intersection(s2)

set([6])

>>>

s1

&s2

set([6])

>>>

s1.intersection_update(s2)

>>>

s1

set([6])

7http://en.wikipedia.org/wiki/intersection_%28set_theory%29

Sym

met

ric

Diff

eren

ce

The

sym

met

ric

diff

eren

ce8

oftw

ose

tsis

the

seto

fele

men

tsw

hich

are

inon

eof

eith

erse

t,bu

tnot

inbo

th.

>>>

s1

=set([4,

6,

9])

>>>

s2

=set([1,

6,

8])

>>>

s1.symmetric_difference(s2)

set([8,

1,

4,

9])

>>>

s1

^s2

set([8,

1,

4,

9])

>>>

s1.symmetric_difference_update(s2)

>>>

s1

set([8,

1,

4,

9])

8http://en.wikipedia.org/wiki/symmetric_difference

SetD

iffer

ence

Pyth

onca

nal

sofin

dth

ese

tdiff

eren

ce9

ofS 1

and

S 2,w

hich

isth

eel

emen

tsth

atar

ein

S 1bu

tnot

inS 2

.

>>>

s1

=set([4,

6,

9])

>>>

s2

=set([1,

6,

8])

>>>

s1.difference(s2)

set([9,

4])

>>>

s1

-s2

set([9,

4])

>>>

s1.difference_update(s2)

>>>

s1

set([9,

4])

9http://en.wikipedia.org/wiki/Complement_%28set_theory%29%

23Relative_Complement

11.0

.10

Mul

tiple

sets

Star

ting

with

Pyth

on2.

6,"u

nion

","i

nter

sect

ion"

,an

d"d

iffer

ence

"ca

nw

ork

with

mul

tiple

inpu

tby

usin

gth

ese

tco

nstr

ucto

r.Fo

rex

ampl

e,us

ing

"set

.inte

rsec

tion(

)":

>>>

s1

=set([3,

6,

7,

9])

>>>

s2

=set([6,

7,

9,

10])

>>>

s3

=set([7,

9,

10,

11])

>>>

set.intersection(s1,

s2,

s3)

set([9,

7])

11.0

.11

froz

ense

t

Afr

ozen

seti

sba

sica

llyth

esa

me

asa

set,

exce

ptth

atit

isim

mut

able

-onc

eit

iscr

eate

d,its

mem

bers

cann

otbe

chan

ged.

Sinc

eth

eyar

eim

mut

able

,the

yar

eal

soha

shab

le,w

hich

mea

nsth

atfr

ozen

sets

can

beus

edas

mem

bers

inot

her

sets

and

asdi

ctio

nary

keys

.fro

zens

ets

have

the

sam

efu

nctio

nsas

norm

alse

ts,

exce

ptno

neof

the

func

tions

that

chan

geth

eco

nten

ts(u

pdat

e,re

mov

e,po

p,et

c.)

are

avai

labl

e.

>>>

fs

=frozenset([2,

3,

4])

>>>

s1

=set([fs,

4,

5,

6])

>>>

s1

set([4,

frozenset([2,

3,

4]),

6,

5])

>>>

fs.intersection(s1)

frozenset([4])

>>>

fs.add(6)

Traceback

(most

recent

call

last):

File

"<stdin>",

line

1,

in

<module>

AttributeError:

'frozenset'

object

has

no

attribute

'add'

11.0

.12

Ref

eren

ce

Pyth

onL

ibra

ryR

efer

ence

onSe

tTyp

es10

10http://docs.python.org/library/stdtypes.html#

set-types-set-frozenset

12O

pera

tors

12.1

Bas

ics

Pyth

onm

ath

wor

kslik

eyo

uw

ould

expe

ct.

>>>

x=

2>>>

y=

3>>>

z=

5>>>

x*y

6 >>>

x+

y5

117

>>>

x*y

+z

11>>>

(x

+y)

*z

25 Not

eth

atPy

thon

adhe

res

toth

ePE

MD

AS

orde

rofo

pera

tions

1 .

12.2

Pow

ers

The

reis

abu

iltin

expo

nent

iatio

nop

erat

or**

,whi

chca

nta

keei

ther

inte

gers

,flo

atin

gpo

into

rcom

plex

num

bers

.Thi

soc

cupi

esits

prop

erpl

ace

inth

eor

der

ofop

erat

ions

.

>>>

2**8

256

1http://en.wikipedia.org/wiki/Order%20of%20operations%20

12.3

Div

isio

nan

dTy

peC

onve

rsio

n

ForP

ytho

n2.

x,di

vidi

ngtw

oin

tege

rsor

long

suse

sint

eger

divi

sion

,als

okn

own

as"fl

oord

ivis

ion"

(app

lyin

gth

eflo

orfu

nctio

n2af

terd

ivis

ion.

So,f

orex

ampl

e,5

/2is

2.U

sing

"/"

todo

divi

sion

this

way

isde

prec

ated

;if

you

wan

tfloo

rdi

visi

on,u

se"/

/"(a

vaila

ble

inPy

thon

2.2

and

late

r).

"/"

does

"tru

edi

visi

on"

forfl

oats

and

com

plex

num

bers

;for

exam

ple,

5.0/

2.0

is2.

5.

ForP

ytho

n3.

x,"/

"do

es"t

rue

divi

sion

"fo

rall

type

s.34

2http://en.wikipedia.org/wiki/Floor%20function

3[http://www.python.org/doc/2.2.3/whatsnew/node7.html

Wha

t'sN

ewin

Pyth

on2.

24

PEP

238

--C

hang

ing

the

Div

isio

nO

pera

tor

ˆ{http://www.python.org/dev/

peps/pep-0238/}

Div

idin

gby

orin

toa

float

ing

poin

tnum

ber

(the

rear

eno

frac

tiona

ltyp

esin

Pyth

on)w

illca

use

Pyth

onto

use

true

divi

sion

.To

coer

cean

inte

gert

obe

com

ea

float

,'flo

at()

'with

the

inte

gera

sa

para

met

er

>>>

x=

5>>>

float(x)

5.0

Thi

sca

nbe

gene

raliz

edfo

roth

ernu

mer

icty

pes:

int(

),co

mpl

ex()

,lon

g().

Bew

are

that

due

toth

elim

itatio

nsof

float

ing

poin

tar

ithm

etic

5 ,ro

undi

nger

rors

can

caus

eun

expe

cted

resu

lts.F

orex

ampl

e:

>>>

print

0.6/0.2

3.0

>>>

print

0.6//0.2

2.0

5http://en.wikipedia.org/wiki/floating%20point

12.4

Mod

ulo

The

mod

ulus

(rem

aind

erof

the

divi

sion

ofth

etw

oop

eran

ds,r

athe

rtha

nth

equ

otie

nt)c

anbe

foun

dus

ing

the

%op

erat

or,o

rby

the

divm

odbu

iltin

func

tion.

The

divm

odfu

nctio

nre

turn

sa

tupl

eco

ntai

ning

the

quot

ient

and

rem

aind

er.

>>>

10%7

3 12.5

Neg

atio

n

Unl

ike

som

eot

herl

angu

ages

,var

iabl

esca

nbe

nega

ted

dire

ctly

:

>>>

x=

5>>>

-x

-5

12.6

Aug

men

ted

Ass

ignm

ent

Ther

eis

shor

than

dfo

rass

igni

ngth

eou

tput

ofan

oper

atio

nto

one

ofth

ein

puts

:

>>>

x=

2>>>

x#

22 >>>

x*=

3>>>

x#

2*3

6 >>>

x+=

4>>>

x#

2*3

+4

10>>>

x/=

5>>>

x#

(2*3

+4)

/5

2 >>>

x**=

2>>>

x#

((2*3

+4)

/5)

**2

4 >>>

x%=

3>>>

x#

((2*3

+4)

/5)

**2

%3

1

>>>

x=

'repeat

this

'>>>

x#

repeat

this

repeat

this

>>>

x*=

3#

fill

with

xrepeated

three

times

>>>

xrepeat

this

repeat

this

repeat

this

12.7

Boo

lean

or:

if

aor

b:

do_this

else: do_this

and:

if

aand

b:

do_this

else: do_this

not:

if

not

a:

do_this

else: do_this

12.8

Ref

eren

ces

13Fl

owco

ntro

l

As

with

mos

tim

pera

tive

lang

uage

s,th

ere

are

thre

em

ain

cate

gorie

sof

prog

ram

flow

cont

rol:

•lo

ops

•br

anch

es•

func

tion

calls

Func

tion

calls

are

cove

red

inth

ene

xtse

ctio

n1 .

1C

hapt

er14

onpa

ge13

9

125

Gen

erat

ors

and

list

com

preh

ensi

ons

are

adva

nced

form

sof

prog

ram

flow

cont

rol,

butt

hey

are

notc

over

edhe

re.

13.0

.1L

oops

InPy

thon

,the

rear

etw

oki

nds

oflo

ops,

'for'

loop

san

d'w

hile

'loo

ps.

For

loop

s

Afo

rlo

opite

rate

sov

erel

emen

tsof

ase

quen

ce(t

uple

orlis

t).

Ava

riab

leis

crea

ted

tore

pres

entt

heob

ject

inth

ese

quen

ce.F

orex

ampl

e,

l=

[100,200,300,400]

for

iin

l:

printi

Thi

sw

illou

tput

100

200

300

400

Thefor

loop

loop

sov

erea

chof

the

elem

ents

ofa

listo

rite

rato

r,as

sign

ing

the

curr

ente

lem

entt

oth

eva

riabl

ena

me

give

n.In

the

first

exam

ple

abov

e,ea

chof

the

elem

ents

inl

isas

sign

edtoi

.

Abu

iltin

func

tion

calle

dra

nge

exis

tsto

mak

ecr

eatin

gse

quen

tiall

ists

such

asth

eon

eab

ove

easi

er.T

helo

opab

ove

iseq

uiva

lent

to:

l=

range(100,

401,100)

for

iin

l:

printi

The

next

exam

ple

uses

ane

gativ

est

ep(th

eth

irdar

gum

entf

orth

ebu

ilt-in

rang

efu

nctio

n):

for

iin

range(10,

0,

-1):

printi

Thi

sw

illou

tput

10

9 8 7 6 5 4 3 2 1

or

for

iin

range(10,

0,

-2):

printi

Thi

sw

illou

tput

10

8 6 4 2

forl

oops

can

have

nam

esfo

reac

hel

emen

tofa

tupl

e,if

itlo

opso

vera

sequ

ence

oftu

ples

.For

inst

ance

l=

[(1,

1),

(2,

4),

(3,

9),

(4,

16),

(5,

25)]

for

x,

xsquared

in

l:

printx,

':',

xsquared

will

outp

ut

1:

12

:4

3:

94

:16

5:

25

Whi

lelo

ops

Aw

hile

loop

repe

ats

ase

quen

ceof

stat

emen

tsun

tilso

me

cond

ition

beco

mes

fals

e.Fo

rexa

mpl

e:

x=

5while

x>

0:

printx

x=

x-

1

Will

outp

ut:

5 4 3 2 1

Pyth

on's

whi

lelo

ops

can

also

have

an'e

lse'

clau

se,w

hich

isa

bloc

kof

stat

e-m

ents

that

isex

ecut

ed(o

nce)

whe

nth

ew

hile

stat

emen

teva

luat

esto

fals

e.Th

ebr

eak

stat

emen

tins

ide

the

whi

lelo

opw

illno

tdir

ectt

hepr

ogra

mflo

wto

the

else

clau

se.F

orex

ampl

e:

x=

5y

=x

while

y>

0:

printy

y=

y-

1else: printx

Thi

sw

illou

tput

:

5 4 3 2 1 5

Unl

ike

som

ela

ngua

ges,

ther

eis

nopo

st-c

ondi

tion

loop

.

Bre

akin

g,co

ntin

uing

and

the

else

clau

seof

loop

s

Pyth

onin

clud

esst

atem

ents

toex

ita

loop

(eith

era

for

loop

ora

whi

lelo

op)

prem

atur

ely.

Toex

ita

loop

,use

the

brea

kst

atem

ent

x=

5while

x>

0:

printx

break

x-=

1printx

this

will

outp

ut

5

The

stat

emen

tto

begi

nth

ene

xtite

ratio

nof

the

loop

with

outw

aitin

gfo

rthe

end

ofth

ecu

rren

tloo

pis

'con

tinue

'.

l=

[5,6,7]

for

xin

l:

continue

printx

Thi

sw

illno

tpro

duce

any

outp

ut.

The

else

clau

seof

loop

sw

illbe

exec

uted

ifno

brea

kst

atem

ents

are

met

inth

elo

op.

l=

range(1,100)

for

xin

l:

ifx

==

100:

printx

break

else: printx,"

is

not

100"

else: print"100

not

found

in

range"

Ano

ther

exam

ple

ofa

whi

lelo

opus

ing

the

brea

kst

atem

ent

and

the

else

stat

emen

t:

expected_str

="melon"

received_str

="apple"

basket

=["banana",

"grapes",

"strawberry",

"melon",

"orange"]

x=

0step

=int(raw_input("Input

iteration

step:

"))

while(received_str

!=

expected_str):

if(x

>=

len(basket)):

print

"No

more

fruits

left

on

the

basket.";

break

received_str

=basket[x]

x+=

step#

Change

this

to

3to

make

the

while

statement

#evaluate

to

false,

avoiding

the

break

statement,

using

the

else

clause.

if(received_str==basket[2]):

print"I

hate",basket[2],"!";

break

if(received_str

!=

expected_str):print

"I

am

waiting

for

my

",expected_str,"."

else: print"Finally

got

what

Iwanted!

my

precious

",expected_str,"!"

print

"Going

back

home

now

!"

Thi

sw

illou

tput

:

Input

iteration

step:

2I

am

waiting

for

my

melon

.I

hate

strawberry

!Going

back

home

now

!

13.0

.2B

ranc

hes

The

reis

basi

cally

only

one

kind

ofbr

anch

inPy

thon

,the

'if's

tate

men

t.T

hesi

mpl

estf

orm

ofth

eif

stat

emen

tsim

ple

exec

utes

abl

ock

ofco

deon

lyif

agi

ven

pred

icat

eis

true

,and

skip

sov

erit

ifth

epr

edic

ate

isfa

lse

Fori

nsta

nce,

>>>

x=

10

>>>

ifx

>0:

...

print"Positive"

...

Positive

>>>

ifx

<0:

...

print"Negative"

...

You

can

also

add

"elif

"(s

hort

for"

else

if")

bran

ches

onto

the

ifst

atem

ent.

Ifth

epr

edic

ate

onth

efir

st“i

f”is

fals

e,it

will

test

the

pred

icat

eon

the

first

elif

,an

dru

nth

atbr

anch

ifit’

str

ue.I

fthe

first

elif

isfa

lse,

ittr

ies

the

seco

ndon

e,an

dso

on.N

ote,

how

ever

,tha

titw

illst

opch

ecki

ngbr

anch

esas

soon

asit

finds

atr

uepr

edic

ate,

and

skip

the

rest

ofth

eif

stat

emen

t.Y

ouca

nal

soen

dyo

urif

stat

emen

tsw

ithan

"els

e"br

anch

.Ifn

one

ofth

eot

herb

ranc

hes

are

exec

uted

,th

enpy

thon

will

run

this

bran

ch.

>>>

x=

-6

>>>

ifx

>0:

...

print"Positive"

...

elifx

==

0:

...

print"Zero"

...

else:

...

print"Negative"

...

'Negative'

13.0

.3C

oncl

usio

n

Any

ofth

ese

loop

s,br

anch

es,a

ndfu

nctio

nca

llsca

nbe

nest

edin

any

way

desi

red.

Alo

opca

nlo

opov

era

loop

,abr

anch

can

bran

chag

ain,

and

afu

nctio

nca

nca

llot

herf

unct

ions

,ore

ven

call

itsel

f.

14Fu

nctio

ns

14.0

.4Fu

nctio

nca

lls

Aca

llabl

eob

ject

isan

obje

ctth

atca

nac

cept

som

ear

gum

ents

(als

oca

lled

para

met

ers)

and

poss

ibly

retu

rnan

obje

ct(o

ften

atu

ple

cont

aini

ngm

ultip

leob

ject

s).

Afu

nctio

nis

the

sim

ples

tcal

labl

eob

ject

inPy

thon

,but

ther

ear

eot

hers

,suc

has

clas

ses1

orce

rtai

ncl

ass

inst

ance

s.

1C

hapt

er19

onpa

ge18

9

139

Defi

ning

func

tions

Afu

nctio

nis

defin

edin

Pyth

onby

the

follo

win

gfo

rmat

:

def

functionname(arg1,

arg2,

...):

statement1

statement2

...

>>>

deffunctionname(arg1,arg2):

...

returnarg1+arg2

...

>>>

t=

functionname(24,24)

#Result:

48

Ifa

func

tion

take

sno

argu

men

ts,

itm

ust

still

incl

ude

the

pare

nthe

ses,

but

with

outa

nyth

ing

inth

em:

def

functionname():

statement1

statement2

...

The

argu

men

tsin

the

func

tion

defin

ition

bind

the

argu

men

tspa

ssed

atfu

nctio

nin

voca

tion

(i.e.

whe

nth

efu

nctio

nis

calle

d),w

hich

are

calle

dac

tual

para

met

ers,

toth

ena

mes

give

nw

hen

the

func

tion

isde

fined

,w

hich

are

calle

dfo

rmal

para

met

ers.

The

inte

rior

ofth

efu

nctio

nha

sno

know

ledg

eof

the

nam

esgi

ven

toth

eac

tual

para

met

ers;

the

nam

esof

the

actu

alpa

ram

eter

sm

ayno

teve

nbe

acce

ssib

le(t

hey

coul

dbe

insi

dean

othe

rfun

ctio

n).

Afu

nctio

nca

n're

turn

'ava

lue,

fore

xam

ple:

def

square(x):

returnx*x

Afu

nctio

nca

nde

fine

varia

bles

with

inth

efu

nctio

nbo

dy,w

hich

are

cons

ider

ed'lo

cal'

toth

efu

nctio

n.T

helo

cals

toge

ther

with

the

argu

men

tsco

mpr

ise

allt

heva

riab

les

with

inth

esc

ope

ofth

efu

nctio

n.A

nyna

mes

with

inth

efu

nctio

nar

eun

boun

dw

hen

the

func

tion

retu

rns

orre

ache

sth

een

dof

the

func

tion

body

.

Dec

lari

ngA

rgum

ents

Def

ault

Arg

umen

tVal

ues

Ifan

yof

the

form

alpa

ram

eter

sin

the

func

tion

defin

ition

are

decl

ared

with

the

form

at"a

rg=

valu

e,"

then

you

will

have

the

optio

nof

nots

peci

fyin

ga

valu

efo

rtho

sear

gum

ents

whe

nca

lling

the

func

tion.

Ifyo

udo

nots

peci

fya

valu

e,th

enth

atpa

ram

eter

will

have

the

defa

ultv

alue

give

nw

hen

the

func

tion

exec

utes

.

>>>

defdisplay_message(message,

truncate_after=4):

...

printmessage[:truncate_after]

...

>>>

display_message("message")

mess

>>>

display_message("message",

6)

messag

Vari

able

-Len

gth

Arg

umen

tLis

ts

Pyth

onal

low

syo

uto

decl

are

two

spec

iala

rgum

ents

whi

chal

low

you

tocr

eate

arbi

trary

-leng

thar

gum

entl

ists

.Thi

smea

nsth

atea

chtim

eyo

uca

llth

efu

nctio

n,yo

uca

nsp

ecif

yan

ynu

mbe

rofa

rgum

ents

abov

ea

cert

ain

num

ber.

def

function(first,second,*remaining):

statement1

statement2

...

Whe

nca

lling

the

abov

efu

nctio

n,yo

um

ustp

rovi

deva

lue

fore

ach

ofth

efir

sttw

oar

gum

ents

.How

ever

,sin

ceth

eth

irdpa

ram

eter

ism

arke

dw

ithan

aste

risk,

any

actu

alpa

ram

eter

saf

tert

hefir

sttw

ow

illbe

pack

edin

toa

tupl

ean

dbo

und

to"r

emai

ning

."

>>>

defprint_tail(first,*tail):

...

printtail

...

>>>

print_tail(1,

5,

2,

"omega")

(5,

2,

'omega')

Ifw

ede

clar

ea

form

alpa

ram

eter

prefi

xed

with

two

aste

risk

s,th

enit

will

bebo

und

toa

dict

iona

ryco

ntai

ning

any

keyw

ord

argu

men

tsin

the

actu

alpa

ram

eter

sw

hich

dono

tcor

resp

ond

toan

yfo

rmal

para

met

ers.

Fore

xam

ple,

cons

ider

the

func

tion:

def

make_dictionary(max_length=10,**entries):

returndict([(key,

entries[key])

fori,

key

in

enumerate(entries.keys())if

i<

max_length])

Ifw

eca

llth

isfu

nctio

nw

ithan

yke

ywor

dar

gum

ents

othe

rtha

nm

ax_l

engt

h,th

eyw

illbe

plac

edin

the

dict

iona

ry"e

ntri

es."

Ifw

ein

clud

eth

eke

ywor

dar

gum

ento

fmax

_len

gth,

itw

illbe

boun

dto

the

form

alpa

ram

eter

max

_len

gth,

asus

ual.

>>>

make_dictionary(max_length=2,

key1=5,

key2=7,

key3=9)

{'key3':

9,

'key2':

7}

Cal

ling

func

tions

Afu

nctio

nca

nbe

calle

dby

appe

ndin

gth

ear

gum

ents

inpa

rent

hese

sto

the

func

tion

nam

e,or

anem

pty

mat

ched

seto

fpar

enth

eses

ifth

efu

nctio

nta

kes

noar

gum

ents

.

foo()

square(3)

bar(5,

x)

Afu

nctio

n's

retu

rnva

lue

can

beus

edby

assi

gnin

git

toa

vari

able

,lik

eso

:

x=

foo()

y=

bar(5,x)

As

show

nab

ove,

whe

nca

lling

afu

nctio

nyo

uca

nsp

ecif

yth

epa

ram

eter

sby

nam

ean

dyo

uca

ndo

soin

any

orde

r

def

display_message(message,

start=0,

end=4):

printmessage[start:end]

display_message("message",

end=3)

This

abov

eis

valid

and

star

twill

beth

ede

faul

tval

ueof

0.A

rest

rictio

npl

aced

onth

isis

afte

rthe

first

nam

edar

gum

entt

hen

alla

rgum

ents

afte

ritm

usta

lso

bena

med

.The

follo

win

gis

notv

alid

display_message(end=5,

start=1,

"my

message")

beca

use

the

thir

dar

gum

ent(

"my

mes

sage

")is

anun

nam

edar

gum

ent.

14.0

.5C

losu

re

Acl

osur

e,al

sokn

own

asne

sted

func

tion

defin

ition

,is

afu

nctio

nde

fined

insi

dean

othe

rfun

ctio

n.Pe

rhap

sbe

stde

scri

bed

with

anex

ampl

e:

>>>

defouter(outer_argument):

...

definner(inner_argument):

...

return

outer_argument

+inner_argument

...

returninner

...

>>>

f=

outer(5)

>>>

f(3)

8 >>>

f(4)

9 Clo

sure

sar

epo

ssib

lein

Pyth

onbe

caus

efu

nctio

nsar

efir

st-c

lass

obje

cts.

Afu

nctio

nis

mer

ely

anob

ject

ofty

pefu

nctio

n.B

eing

anob

ject

mea

nsit

ispo

ssib

leto

pass

afu

nctio

nob

ject

(an

unca

lled

func

tion)

arou

ndas

argu

men

tor

asre

turn

valu

eor

toas

sign

anot

hern

ame

toth

efu

nctio

nob

ject

.Aun

ique

feat

ure

that

mak

escl

osur

eus

eful

isth

atth

een

clos

edfu

nctio

nm

ayus

eth

ena

mes

defin

edin

the

pare

ntfu

nctio

n's

scop

e.

lam

bda

lam

bda

isan

anon

ymou

s(u

nnam

ed)f

unct

ion.

Itis

used

prim

arily

tow

rite

very

shor

tfun

ctio

nsth

atar

ea

hass

leto

defin

ein

the

norm

alw

ay.A

func

tion

like

this

:

>>>

defadd(a,

b):

...

returna

+b

...

>>>

add(4,

3)

7 may

also

bede

fined

usin

gla

mbd

a

>>>

print(lambda

a,

b:

a+

b)(4,

3)

7 Lam

bda

isof

ten

used

asan

argu

men

tto

othe

rfun

ctio

nsth

atex

pect

sa

func

tion

obje

ct,s

uch

asso

rted

()'s

'key

'arg

umen

t.

>>>

sorted([[3,

4],

[3,

5],

[1,

2],

[7,

3]],

key=lambdax:

x[1])

[[1,

2],

[7,

3],

[3,

4],

[3,

5]]

The

lam

bda

form

isof

ten

usef

ulas

acl

osur

e,su

chas

illus

trate

din

the

follo

win

gex

ampl

e:

>>>

defattribution(name):

...

return

lambda

x:

x+

'--

'+

name

...

>>>

pp

=attribution('John')

>>>

pp('Dinner

is

in

the

fridge')

'Dinner

is

in

the

fridge

--

John'

note

that

the

lam

bda

func

tion

can

use

the

valu

esof

vari

able

sfr

omth

esc

ope2

inw

hich

itw

ascr

eate

d(l

ike

pre

and

post

).T

his

isth

ees

senc

eof

clos

ure.

2C

hapt

er15

onpa

ge15

1

de:P

ytho

n-Pr

ogra

mm

ieru

ng:_

Funk

tione

n3es

:Inm

ersi

ónen

Pyth

on/S

upr

imer

prog

ram

aen

Pyth

on/D

ecla

raci

ónde

func

ione

s4fr

:Pro

gram

mat

ion_

-Py

thon

/Fon

ctio

n5pt

:Pyt

hon/

Con

ceito

sbá

sico

s/Fu

nçõe

s6

3http://de.wikibooks.org/wiki/Python-Programmierung%3A_

Funktionen

4http://es.wikibooks.org/wiki/Inmersi%F3n%20en%20Python%

2FSu%20primer%20programa%20en%20Python%2FDeclaraci%F3n%

20de%20funciones

5http://fr.wikibooks.org/wiki/Programmation_Python%

2FFonction

6http://pt.wikibooks.org/wiki/Python%2FConceitos%20b%

E1sicos%2FFun%E7%F5es

15Sc

opin

g

15.0

.6Va

riab

les

Var

iabl

esin

Pyth

onar

eau

tom

atic

ally

decl

ared

byas

sign

men

t.V

aria

bles

are

alw

ays

refe

renc

esto

obje

cts,

and

are

neve

rtyp

ed.V

aria

bles

exis

tonl

yin

the

curr

ents

cope

orgl

obal

scop

e.W

hen

they

goou

tof

scop

e,th

eva

riab

les

are

dest

roye

d,bu

tthe

obje

cts

tow

hich

they

refe

rar

eno

t(un

less

the

num

ber

ofre

fere

nces

toth

eob

ject

drop

sto

zero

).

Scop

eis

delin

eate

dby

func

tion

and

clas

sbl

ocks

.B

oth

func

tions

and

thei

rsc

opes

can

bene

sted

.So

ther

efor

e

151

def

foo():

defbar():

x=

5#

xis

now

in

scope

returnx

+y

#y

is

defined

in

the

enclosing

scope

later

y=

10

returnbar()

#now

that

yis

defined,

bar's

scope

includes

y

Now

whe

nth

isco

deis

test

ed,

>>>

foo()

15

>>>

bar()

Traceback

(most

recent

call

last):

File

"<pyshell#26>",

line

1,

in

-toplevel-

bar()

NameError:

name

'bar'

is

not

defined

The

nam

e'b

ar'i

sno

tfou

ndbe

caus

ea

high

ersc

ope

does

noth

ave

acce

ssto

the

nam

eslo

wer

inth

ehi

erar

chy.

Itis

aco

mm

onpi

tfal

lto

fail

tolo

okup

anat

trib

ute

(suc

has

am

etho

d)of

anob

ject

(suc

has

aco

ntai

ner)

refe

renc

edby

ava

riab

lebe

fore

the

vari

able

isas

sign

edth

eob

ject

.In

itsm

ostc

omm

onfo

rm:

>>>

forx

in

range(10):

y.append(x)

#append

is

an

attribute

of

lists

Traceback

(most

recent

call

last):

File

"<pyshell#46>",

line

2,

in

-toplevel-

y.append(x)

NameError:

name

'y'

is

not

defined

Her

e,to

corr

ectt

his

prob

lem

,one

mus

tadd

y=

[]be

fore

the

forl

oop.

16E

xcep

tions

Pyth

onha

ndle

sal

lerr

ors

with

exce

ptio

ns.

An

exce

ptio

nis

asi

gnal

that

aner

roro

roth

erun

usua

lcon

ditio

nha

soc

curr

ed.

The

rear

ea

num

ber

ofbu

ilt-i

nex

cept

ions

,w

hich

indi

cate

cond

ition

slik

ere

adin

gpa

stth

een

dof

afil

e,or

divi

ding

byze

ro.

You

can

also

defin

eyo

urow

nex

cept

ions

.

155

16.0

.7R

aisi

ngex

cept

ions

Whe

neve

ryou

rpro

gram

atte

mpt

sto

doso

met

hing

erro

neou

sor

mea

ning

less

,Py

thon

rais

esex

cept

ion

tosu

chco

nduc

t:

>>>

1/

0Traceback

(most

recent

call

last):

File

"<stdin>",

line

1,

in

?ZeroDivisionError:

integer

division

or

modulo

by

zero

Thi

str

aceb

ack

indi

cate

sth

atth

eZ

eroD

ivis

ionE

rror

exce

ptio

nis

bein

gra

ised

.T

his

isa

built

-in

exce

ptio

n--

see

belo

wfo

ralis

tofa

llth

eot

hero

nes.

16.0

.8C

atch

ing

exce

ptio

ns

Inor

der

toha

ndle

erro

rs,y

ouca

nse

tup

exce

ptio

nha

ndlin

gbl

ocks

inyo

urco

de.

The

keyw

ords

try

and

exce

ptar

eus

edto

catc

hex

cept

ions

.W

hen

an

erro

rocc

urs

with

inth

etr

ybl

ock,

Pyth

onlo

oks

fora

mat

chin

gex

cept

bloc

kto

hand

leit.

Ifth

ere

ison

e,ex

ecut

ion

jum

psth

ere.

Ifyo

uex

ecut

eth

isco

de:

try:print1/0

except

ZeroDivisionError:

print"You

can't

divide

by

zero,

you're

silly."

The

nPy

thon

will

prin

tthi

s:

You

can't

divide

by

zero,

you're

silly.

Ifyo

udo

n'ts

peci

fyan

exce

ptio

nty

peon

the

exce

ptlin

e,it

will

chee

rful

lyca

tch

alle

xcep

tions

.Thi

sis

gene

rally

aba

did

eain

prod

uctio

nco

de,s

ince

itm

eans

your

prog

ram

will

blis

sful

lyig

nore

unex

pect

eder

rors

asw

ella

son

esw

hich

the

exce

ptbl

ock

isac

tual

lypr

epar

edto

hand

le.

Exc

eptio

nsca

npr

opag

ate

upth

eca

llst

ack:

def

f(x):

returng(x)

+1

def

g(x):

ifx

<0:raise

ValueError,

"I

can't

cope

with

anegative

number

here."else:return

5

try:printf(-6)

except

ValueError:

print"That

value

was

invalid."

Inth

isco

de,

the

prin

tst

atem

ent

calls

the

func

tion

f.T

hat

func

tion

calls

the

func

tion

g,w

hich

will

rais

ean

exce

ptio

nof

type

Val

ueE

rror

.N

eith

erf

nor

gha

sa

try/

exce

ptbl

ock

toha

ndle

Val

ueE

rror

.So

the

exce

ptio

nra

ised

prop

agat

esou

tto

the

mai

nco

de,w

here

ther

eis

anex

cept

ion-

hand

ling

bloc

kw

aitin

gfo

rit.

Thi

sco

depr

ints

:

That

value

was

invalid.

Som

etim

esit

isus

eful

tofin

dou

texa

ctly

wha

twen

twro

ng,o

rto

prin

tthe

pyth

oner

rort

exty

ours

elf.

Fore

xam

ple:

try: the_file

=open("the_parrot")

exceptIOError,

(ErrorNumber,

ErrorMessage):

ifErrorNumber

==

2:#

file

not

found

print"Sorry,

'the_parrot'

has

apparently

joined

the

choir

invisible."

else:print"Congratulation!

you

have

managed

to

trip

a#%d

error"

%ErrorNumber

printErrorMessage

Whi

chof

cour

sew

illpr

int:

Sorry,

'the_parrot'

has

apparently

joined

the

choir

invisible.

Cus

tom

Exc

eptio

ns

Cod

esi

mila

rto

that

seen

abov

eca

nbe

used

tocr

eate

cust

omex

cept

ions

and

pass

info

rmat

ion

alon

gw

ithth

em.T

his

can

beex

trem

ely

usef

ulw

hen

tryi

ngto

debu

gco

mpl

icat

edpr

ojec

ts.H

ere

isho

wth

atco

dew

ould

look

;firs

tcre

atin

gth

ecu

stom

exce

ptio

ncl

ass:

classCustomException(Exception):

def__init__(self,

value):

self.parameter

=value

def__str__(self):

return

repr(self.parameter)

And

then

usin

gth

atex

cept

ion:

try:raiseCustomException("My

Useful

Error

Message")

except

CustomException,

(instance):

print"Caught:

"+

instance.parameter

Tryi

ngov

eran

dov

erag

ain

16.0

.9R

ecov

erin

gan

dco

ntin

uing

with

final

ly

Exce

ptio

nsco

uld

lead

toa

situ

atio

nw

here

,afte

rrai

sing

anex

cept

ion,

the

code

bloc

kw

here

the

exce

ptio

noc

curr

edm

ight

notb

ere

visi

ted.

Inso

me

case

sth

ism

ight

leav

eex

tern

alre

sour

ces

used

byth

epr

ogra

min

anun

know

nst

ate.

finally

clau

seal

low

spr

ogra

mm

ers

tocl

ose

such

reso

urce

sin

case

ofan

exce

ptio

n.B

etw

een

2.4

and

2.5

vers

ion

ofpy

thon

ther

eis

chan

geof

synt

axfo

rfinally

clau

se.

•Py

thon

2.4

try:result

=None

try: result

=x/y

exceptZeroDivisionError:

print"division

by

zero!"

print"result

is

",

result

finally:

print"executing

finally

clause"

•Py

thon

2.5

try:result

=x

/y

except

ZeroDivisionError:

print"division

by

zero!"

else:print"result

is",

result

finally:

print"executing

finally

clause"

16.0

.10

Bui

lt-in

exce

ptio

ncl

asse

s

All

built

-in

Pyth

onex

cept

ions

1

16.0

.11

Exo

ticus

esof

exce

ptio

ns

Exc

eptio

nsar

ego

odfo

rmor

eth

anju

ster

rorh

andl

ing.

Ifyo

uha

vea

com

pli-

cate

dpi

ece

ofco

deto

choo

sew

hich

ofse

vera

lcou

rses

ofac

tion

tota

ke,i

tcan

beus

eful

tous

eex

cept

ions

toju

mp

outo

fth

eco

deas

soon

asth

ede

cisi

onca

nbe

mad

e.T

hePy

thon

-bas

edm

ailin

glis

tsof

twar

eM

ailm

ando

esth

isin

deci

ding

how

am

essa

gesh

ould

beha

ndle

d.U

sing

exce

ptio

nslik

eth

ism

ayse

emlik

eit'

sa

sort

ofG

OT

O--

and

inde

edit

is,b

uta

limite

don

eca

lled

anes

cape

cont

inua

tion.

Con

tinua

tions

are

apo

wer

fulf

unct

iona

l-pr

ogra

mm

ing

tool

and

itca

nbe

usef

ulto

lear

nth

em.

1http://docs.python.org/library/exceptions.html

Just

asa

sim

ple

exam

ple

ofho

wex

cept

ions

mak

epr

ogra

mm

ing

easi

er,s

ayyo

uw

antt

oad

dite

ms

toa

listb

utyo

udo

n'tw

antt

ous

e"i

f"st

atem

ents

toin

itial

ize

the

listw

eco

uld

repl

ace

this

:

if

hasattr(self,

'items'):

self.items.extend(new_items)

else: self.items

=list(new_items)

Usi

ngex

cept

ions

,we

can

emph

asiz

eth

eno

rmal

prog

ram

flow

—th

atus

ually

we

just

exte

ndth

elis

t—ra

ther

than

emph

asiz

ing

the

unus

ualc

ase:

try:self.items.extend(new_items)

except

AttributeError:

self.items

=list(new_items)

17In

puta

ndou

tput

17.1

Inpu

t

Pyth

onha

stw

ofu

nctio

nsde

sign

edfo

racc

eptin

gda

tadi

rect

lyfr

omth

eus

er:

•input()

•raw_input()

The

rear

eal

sove

rysi

mpl

ew

ays

ofre

adin

ga

file

and,

fors

tric

terc

ontr

olov

erin

put,

read

ing

from

stdi

nif

nece

ssar

y.

165

17.1

.1ra

w_i

nput

()

raw

_inp

ut()

asks

the

user

for

ast

ring

ofda

ta(e

nded

with

ane

wlin

e),

and

sim

ply

retu

rns

the

strin

g.It

can

also

take

anar

gum

ent,

whi

chis

disp

laye

das

apr

ompt

befo

reth

eus

eren

ters

the

data

.E.g

.

print

raw_input('What

is

your

name?

')

prin

tsou

t

What

is

your

name?

<user

input

data

here>

Exa

mpl

e:in

orde

rto

assi

gnth

eus

er's

nam

e,i.e

.str

ing

data

,to

ava

riab

le"x

"yo

uw

ould

type

x=

raw_input('What

is

your

name?')

Onc

eth

eus

erin

puts

his

nam

e,e.

g.Si

mon

,you

can

call

itas

x

print

('Your

name

is

'+

x)

prin

tsou

t

Your

name

is

Simon

Not

e:in

3.x

"...r

aw_i

nput

()w

asre

nam

edto

inpu

t().

Tha

tis

,th

ene

win

put(

)fu

nctio

nre

ads

alin

efr

omsy

s.st

din

and

retu

rns

itw

ithth

etr

ailin

gne

wlin

est

ripp

ed.I

trai

ses

EO

FErr

orif

the

inpu

tis

term

inat

edpr

emat

urel

y.To

get

the

old

beha

vior

ofin

put(

),us

eev

al(i

nput

())."

17.1

.2in

put(

)

inpu

t()u

ses

raw

_inp

utto

read

ast

ring

ofda

ta,a

ndth

enat

tem

pts

toev

alua

teit

asif

itw

ere

aPy

thon

prog

ram

,and

then

retu

rns

the

valu

eth

atre

sults

.So

ente

ring

[1,2,3]

wou

ldre

turn

alis

tcon

tain

ing

thos

enu

mbe

rs,j

usta

sif

itw

ere

assi

gned

dire

ctly

inth

ePy

thon

scri

pt.

Mor

eco

mpl

icat

edex

pres

sion

sar

epo

ssib

le.F

orex

ampl

e,if

asc

ript

says

:

x=

input('What

are

the

first

10

perfect

squares?

')

itis

poss

ible

fora

user

toin

put:

map(lambdax:

x*x,

range(10))

whi

chyi

elds

the

corr

ecta

nsw

erin

listf

orm

.Not

eth

atno

inpu

tted

stat

emen

tca

nsp

anm

ore

than

one

line.

inpu

t()s

houl

dno

tbe

used

fora

nyth

ing

butt

hem

ostt

rivia

lpro

gram

.Tur

ning

the

stri

ngs

retu

rned

from

raw

_inp

ut()

into

pyth

onty

pes

usin

gan

idio

msu

chas

:

x=

None

while

not

x:

try:x

=int(raw_input())

exceptValueError:

print'Invalid

Number'

ispr

efer

able

,as

inpu

t()

uses

eval

()to

turn

alit

eral

into

apy

thon

type

.T

his

will

allo

wa

mal

icio

uspe

rson

toru

nar

bitr

ary

code

from

insi

deyo

urpr

ogra

mtr

ivia

lly.

17.1

.3Fi

leIn

put

File

Obj

ects

Pyth

onin

clud

esa

built

-infil

ety

pe.F

iles

can

beop

ened

byus

ing

the

file

type

'sco

nstr

ucto

r:

f=

file('test.txt',

'r')

Thi

sm

eans

fis

open

forr

eadi

ng.T

hefir

star

gum

enti

sth

efil

enam

ean

dth

ese

cond

para

met

eris

the

mod

e,w

hich

can

be'r'

,'w

',or

'rw',

amon

gso

me

othe

rs.

The

mos

tcom

mon

way

tore

adfr

oma

file

issi

mpl

yto

itera

teov

erth

elin

esof

the

file:

f=

open('test.txt',

'r')

for

line

in

f:

printline[0]

f.close()

Thi

sw

illpr

intt

hefir

stch

arac

tero

feac

hlin

e.N

ote

that

ane

wlin

eis

atta

ched

toth

een

dof

each

line

read

this

way

.

Bec

ause

files

are

auto

mat

ical

lycl

osed

whe

nth

efil

eob

ject

goes

outo

fsco

pe,

ther

eis

nore

alne

edto

clos

eth

emex

plic

itly.

So,t

helo

opin

the

prev

ious

code

can

also

bew

ritte

nas

:

for

line

in

open('test.txt',

'r'):

printline[0]

Itis

also

poss

ible

tore

adlim

ited

num

bers

ofch

arac

ters

ata

time,

like

so:

c=

f.read(1)

while

len(c)

>0:

iflen(c.strip())

>0:print

c,

c=

f.read(1)

This

will

read

the

char

acte

rsfr

omfo

neat

atim

e,an

dth

enpr

intt

hem

ifth

ey're

notw

hite

spac

e.

Afil

eob

ject

impl

icitl

yco

ntai

nsa

mar

kert

ore

pres

entt

hecu

rren

tpos

ition

.If

the

file

mar

kers

houl

dbe

mov

edba

ckto

the

begi

nnin

g,on

eca

nei

ther

clos

eth

efil

eob

ject

and

reop

enit

orju

stm

ove

the

mar

kerb

ack

toth

ebe

ginn

ing

with

:

f.seek(0)

Stan

dard

File

Obj

ects

Like

man

yot

herl

angu

ages

,the

rear

ebu

ilt-in

file

obje

cts

repr

esen

ting

stan

dard

inpu

t,ou

tput

,an

der

ror.

The

sear

ein

the

sys

mod

ule

and

are

calle

dst

din,

stdo

ut,

and

stde

rr.

The

rear

eal

soim

mut

able

copi

esof

thes

ein

__st

din_

_,__

stdo

ut__

,and

__st

derr

__.

Thi

sis

for

IDL

Ean

dot

her

tool

sin

whi

chth

est

anda

rdfil

esha

vebe

ench

ange

d.

You

mus

tim

port

the

sys

mod

ule

tous

eth

esp

ecia

lstd

in,s

tdou

t,st

derr

I/O

hand

les.

import

sys

For

finer

cont

rolo

ver

inpu

t,us

esy

s.st

din.

read

().

Inor

der

toim

plem

entt

heU

NIX

'cat

'pro

gram

inPy

thon

,you

coul

ddo

som

ethi

nglik

eth

is:

import

sys

for

line

in

sys.stdin:

printline,

Not

eth

atsy

s.st

din.

read

()w

illre

adfr

omst

anda

rdin

putt

illE

OF.

(whi

chis

usua

llyC

trl+

D.)

Als

oim

port

ant

isth

esy

s.ar

gvar

ray.

sys.

argv

isan

arra

yth

atco

ntai

nsth

eco

mm

and-

line

argu

men

tspa

ssed

toth

epr

ogra

m.

python

program.py

hello

there

programmer!

Thi

sar

ray

can

bein

dexe

d,an

dth

ear

gum

ents

eval

uate

d.In

the

abov

eex

ampl

e,sy

s.ar

gv[2

]wou

ldco

ntai

nth

est

ring

"the

re",

beca

use

the

nam

eof

the

prog

ram

("pr

ogra

m.p

y")

isst

ored

inar

gv[0

].Fo

rm

ore

com

plic

ated

com

man

d-lin

ear

gum

entp

roce

ssin

g,se

eth

e"a

rgpa

rse"

mod

ule.

17.2

Out

put

The

basi

cw

ayto

doou

tput

isth

epr

ints

tate

men

t.

print('Hello,

world')

Thi

sco

deou

ghtt

obe

obvi

ous.

Inor

dert

opr

intm

ultip

leth

ings

onth

esa

me

line,

use

com

mas

betw

een

them

,lik

eso

:

print('Hello,',

'World')

Thi

sw

illpr

into

utth

efo

llow

ing:

Hello,

World

Not

eth

atal

thou

ghne

ither

stri

ngco

ntai

ned

asp

ace,

asp

ace

was

adde

dby

the

prin

tsta

tem

entb

ecau

seof

the

com

ma

betw

een

the

two

obje

cts.

Arb

itrar

yda

taty

pes

can

bepr

inte

dth

isw

ay:

print

1,2,0xff,0777,(10+5j),-0.999,map,sys

Thi

sw

illpr

into

ut:

12

255

511

(10+5j)

-0.999

<built-in

function

map>

<module

'sys'

(built-in)>

Obj

ects

can

bepr

inte

don

the

sam

elin

ew

ithou

tnee

ding

tobe

onth

esa

me

line

ifon

epu

tsa

com

ma

atth

een

dof

apr

ints

tate

men

t:

for

iin

range(10):

printi,

will

outp

ut:

01

23

45

67

89

Inor

dert

oen

dth

islin

e,it

may

bene

cess

ary

toad

da

prin

tsta

tem

entw

ithou

tan

yob

ject

s.

for

iin

range(10):

printi,

print

for

iin

range(10,20):

printi,

will

outp

ut:

01

23

45

67

89

10

11

12

13

14

15

16

17

18

19

Ifth

eba

repr

ints

tate

men

twer

eno

tpre

sent

,the

abov

eou

tput

wou

ldlo

oklik

e:

01

23

45

67

89

10

11

12

13

14

15

16

17

18

19

17.2

.1Pr

intin

gw

ithou

tcom

mas

orne

wlin

es

Ifit

isno

tdes

irab

leto

add

spac

esbe

twee

nob

ject

s,bu

tyou

wan

tto

run

them

allt

oget

hero

non

elin

e,th

ere

are

seve

ralt

echn

ique

sfo

rdoi

ngth

at.

conc

aten

atio

n

Con

cate

nate

the

strin

gre

pres

enta

tions

ofea

chob

ject

,the

nla

terp

rintt

hew

hole

thin

gat

once

.

print

str(1

)+str(2)+str(0xff)+str(0777)+str(10+5j)+str(-0.999)+str(map)+str(sys)

will

outp

ut:

12255511(10+5j)-0.999<built-in

function

map><module

'sys'

(built-in)>

wri

te

you

can

mak

ea

shor

than

dfo

rsys

.std

out.w

rite

and

use

that

foro

utpu

t.

import

sys

write

=sys.stdout.write

write('20')

write('05\n')

will

outp

ut:

2005

You

may

need

sys.

stdo

ut.fl

ush(

)to

gett

hatt

exto

nth

esc

reen

quic

kly.

Itis

also

poss

ible

tous

esi

mila

rsy

ntax

whe

nw

ritin

gto

afil

e,in

stea

dof

tost

anda

rdou

tput

,lik

eso

:

print

>>

f,

'Hello,

world'

Thi

sw

illpr

int

toan

yob

ject

that

impl

emen

tsw

rite

(),

whi

chin

clud

esfil

eob

ject

s.

18M

odul

es

Mod

ules

are

asi

mpl

ew

ayto

stru

ctur

ea

prog

ram

.Mos

tly,t

here

are

mod

ules

inth

est

anda

rdlib

rary

and

ther

ear

eot

herP

ytho

nfil

es,o

rdir

ecto

ries

cont

aini

ngPy

thon

files

,in

the

curr

entd

irect

ory

(eac

hof

whi

chco

nstit

ute

am

odul

e).Y

ouca

nal

soin

stru

ctPy

thon

tose

arch

othe

rdi

rect

orie

sfo

rm

odul

esby

plac

ing

thei

rpat

hsin

the

PYT

HO

NPA

TH

envi

ronm

entv

aria

ble.

18.1

Impo

rtin

ga

Mod

ule

Mod

ules

inPy

thon

are

used

byim

port

ing

them

.For

exam

ple,

181

import

math

Thi

sim

port

sth

em

ath

stan

dard

mod

ule.

All

ofth

efu

nctio

nsin

that

mod

ule

are

nam

espa

ced

byth

em

odul

ena

me,

i.e.

import

math

print

math.sqrt(10)

Thi

sis

ofte

na

nuis

ance

,so

othe

rsyn

taxe

sar

eav

aila

ble

tosi

mpl

ify

this

,

from

string

import

whitespace

from

math

import

*from

math

import

sin

as

SIN

from

math

import

cos

as

COS

from

ftplib

import

FTP

as

ftp_connection

print

sqrt(10)

The

first

stat

emen

tmea

nsw

hite

spac

eis

adde

dto

the

curr

ents

cope

(but

noth

-in

gel

seis

).T

hese

cond

stat

emen

tmea

nsth

atal

lthe

elem

ents

inth

em

ath

nam

espa

ceis

adde

dto

the

curr

ents

cope

.

Mod

ules

can

beth

ree

diff

eren

tkin

dsof

thin

gs:

•Py

thon

files

•Sh

ared

Obj

ects

(und

erU

nix

and

Lin

ux)w

ithth

e.s

osu

ffix

•D

LL

's(u

nder

Win

dow

s)w

ithth

e.p

ydsu

ffix

•di

rect

orie

s

Mod

ules

are

load

edin

the

orde

rthe

y're

foun

d,w

hich

isco

ntro

lled

bysy

s.pa

th.

The

curr

entd

irec

tory

isal

way

son

the

path

.

Dir

ecto

ries

shou

ldin

clud

ea

file

inth

emca

lled

__in

it__.

py,

whi

chsh

ould

prob

ably

incl

ude

the

othe

rfile

sin

the

dire

ctor

y.

Cre

atin

ga

DL

Lth

atin

terf

aces

with

Pyth

onis

cove

red

inan

othe

rsec

tion.

18.2

Cre

atin

ga

Mod

ule

18.2

.1Fr

oma

File

The

easi

estw

ayto

crea

tea

mod

ule

byha

ving

afil

eca

lled

mym

od.p

yei

ther

ina

dire

ctor

yre

cogn

ized

byth

ePY

TH

ON

PAT

Hva

riab

leor

(eve

nea

sier

)in

the

sam

edi

rect

ory

whe

reyo

uar

ew

orki

ng.

Ifyo

uha

veth

efo

llow

ing

file

mym

od.p

y

class

Object1:

def__init__(self):

self.name

='object

1'

you

can

alre

ady

impo

rtth

is"m

odul

e"an

dcr

eate

inst

ance

sof

the

obje

ctO

b-je

ct1.

import

mymod

myobject

=mymod.Object1()

from

mymod

import

*myobject

=Object1()

18.2

.2Fr

oma

Dir

ecto

ry

Itis

notf

easi

ble

for

larg

erpr

ojec

tsto

keep

allc

lass

esin

asi

ngle

file.

Itis

ofte

nea

sier

tost

ore

allfi

les

indi

rect

orie

san

dlo

adal

lfile

sw

ithon

eco

mm

and.

Eac

hdi

rect

ory

need

sto

have

a__init__.py

file

whi

chco

ntai

nspy

thon

com

man

dsth

atar

eex

ecut

edup

onlo

adin

gth

edi

rect

ory.

Supp

ose

we

have

two

mor

eob

ject

sca

lledObject2

andObject3

and

we

wan

tto

load

allt

hree

obje

cts

with

one

com

man

d.W

eth

encr

eate

adi

rect

ory

calle

dm

ymod

and

we

stor

eth

ree

files

calle

dObject1.py

,Object2.py

andObject3.py

init.

Thes

efil

esw

ould

then

cont

ain

one

obje

ctpe

rfile

but

this

notr

equi

red

(alth

ough

itad

dscl

arity

).W

ew

ould

then

wri

teth

efo

llow

ing

__init__.py

file:

from

Object1

import

*

from

Object2

import

*from

Object3

import

*

__all__

=["Object1",

"Object2",

"Object3"]

The

first

thre

eco

mm

ands

tell

pyth

onw

hatt

odo

whe

nso

meb

ody

load

sth

em

odul

e.T

hela

stst

atem

ent

defin

ing

__al

l__t

ells

pyth

onw

hat

todo

whe

nso

meb

ody

exec

utes

from

mym

odim

port

*.U

sual

lyw

ew

antt

ous

epa

rts

ofa

mod

ule

inot

her

part

sof

am

odul

e,e.

g.w

ew

antt

ous

eO

bjec

t1in

Obj

ect2

.W

eca

ndo

this

easi

lyw

ithan

from

.im

port

*co

mm

and

asth

efo

llow

ing

file

Obj

ect2

.py

show

s:

from

.import

*

class

Object2:

def__init__(self):

self.name

='object

2'

self.otherObject

=Object1()

We

can

now

star

tpyt

hon

and

impo

rtm

ymod

asw

eha

vein

the

prev

ious

sect

ion.

18.3

Ext

erna

llin

ks

•Py

thon

Doc

umen

tatio

n1

1http://docs.python.org/tutorial/modules.html

19C

lass

es

Cla

sses

are

aw

ayof

aggr

egat

ing

sim

ilard

ata

and

func

tions

.Acl

assi

sbas

ical

lya

scop

ein

side

whi

chva

rious

code

(esp

ecia

llyfu

nctio

nde

finiti

ons)

isex

ecut

ed,

and

the

loca

lsto

this

scop

ebe

com

eat

trib

utes

ofth

ecl

ass,

and

ofan

yob

ject

sco

nstru

cted

byth

iscl

ass.

An

obje

ctco

nstru

cted

bya

clas

sis

calle

dan

inst

ance

ofth

atcl

ass.

19.0

.1D

efini

nga

Cla

ss

Tode

fine

acl

ass,

use

the

follo

win

gfo

rmat

:

189

class

ClassName:

...

...

The

capi

taliz

atio

nin

this

clas

sde

finiti

onis

the

conv

entio

n,bu

tis

notr

equi

red

byth

ela

ngua

ge.

19.0

.2In

stan

ceC

onst

ruct

ion

The

clas

sis

aca

llabl

eob

ject

that

cons

truc

tsan

inst

ance

ofth

ecl

ass

whe

nca

lled.

Toco

nstr

ucta

nin

stan

ceof

the

clas

s,Fo

o,"c

all"

the

clas

sob

ject

:

f=

Foo()

Thi

sco

nstr

ucts

anin

stan

ceof

clas

sFo

oan

dcr

eate

sa

refe

renc

eto

itin

f.

19.0

.3C

lass

Mem

bers

Inor

dert

oac

cess

the

mem

bero

fan

inst

ance

ofa

clas

s,us

eth

esy

ntax

<cla

ssin

stan

ce>.

<mem

ber>

.It

isal

sopo

ssib

leto

acce

ssth

em

embe

rsof

the

clas

sde

finiti

onw

ith<c

lass

nam

e>.<

mem

ber>

.

Met

hods

Am

etho

dis

afu

nctio

nw

ithin

acl

ass.

The

first

argu

men

t(m

etho

dsm

ust

alw

ays

take

atle

asto

near

gum

ent)

isal

way

sth

ein

stan

ceof

the

clas

son

whi

chth

efu

nctio

nis

invo

ked.

Fore

xam

ple

>>>

classFoo:

...

defsetx(self,

x):

...

self.x

=x

...

defbar(self):

...

print

self.x

Ifth

isco

dew

ere

exec

uted

,not

hing

wou

ldha

ppen

,atl

east

until

anin

stan

ceof

Foo

wer

eco

nstr

ucte

d,an

dth

enba

rwer

eca

lled

onth

atin

stan

ce.

Invo

king

Met

hods

Cal

ling

am

etho

dis

muc

hlik

eca

lling

afu

nctio

n,bu

tins

tead

ofpa

ssin

gth

ein

stan

ceas

the

first

para

met

erlik

eth

elis

toff

orm

alpa

ram

eter

ssu

gges

ts,u

seth

efu

nctio

nas

anat

trib

ute

ofth

ein

stan

ce.

>>>

f.setx(5)

>>>

f.bar()

Thi

sw

illou

tput

5

Itis

poss

ible

toca

llth

em

etho

don

anar

bitra

ryob

ject

,by

usin

git

asan

attri

bute

ofth

ede

finin

gcl

ass

inst

ead

ofan

inst

ance

ofth

atcl

ass,

like

so:

>>>

Foo.setx(f,5)

>>>

Foo.bar(f)

Thi

sw

illha

veth

esa

me

outp

ut.

Dyn

amic

Cla

ssSt

ruct

ure

As

show

nby

the

met

hod

setx

abov

e,th

em

embe

rsof

aPy

thon

clas

sca

nch

ange

durin

gru

ntim

e,no

tjus

tthe

irva

lues

,unl

ike

clas

ses

inla

ngua

ges

like

Cor

Java

.W

eca

nev

ende

lete

f.xaf

terr

unni

ngth

eco

deab

ove.

>>>

delf.x

>>>

f.bar()

Traceback

(most

recent

call

last):

File

"<stdin>",

line

1,

in

?File

"<stdin>",

line

5,

in

bar

AttributeError:

Foo

instance

has

no

attribute

'x'

Ano

ther

effe

ctof

this

isth

atw

eca

nch

ange

the

defin

ition

ofth

eFo

ocl

ass

duri

ngpr

ogra

mex

ecut

ion.

Inth

eco

debe

low

,we

crea

tea

mem

bero

fthe

Foo

clas

sde

finiti

onna

med

y.If

we

then

crea

tea

new

inst

ance

ofFo

o,it

will

now

have

this

new

mem

ber.

>>>

Foo.y

=10

>>>

g=

Foo()

>>>

g.y

10 Vie

win

gC

lass

Dic

tiona

ries

At

the

hear

tof

all

this

isa

dict

iona

ry1

that

can

beac

cess

edby

"var

s(C

lass

Nam

e)"

>>>

vars(g)

{} Atfi

rst,

this

outp

utm

akes

nose

nse.

We

just

saw

that

gha

dth

em

embe

ry,s

ow

hyis

n'ti

tin

the

mem

berd

ictio

nary

?If

you

rem

embe

r,th

ough

,we

puty

inth

ecl

ass

defin

ition

,Foo

,not

g.

>>>

vars(Foo)

{'y':

10,

'bar':

<function

bar

at

0x4d6a3c>,

'__module__':

'__main__',

'setx':

<function

setx

at

0x4d6a04>,

'__doc__':

None}

And

ther

ew

eha

veal

lthe

mem

bers

ofth

eFo

ocl

ass

defin

ition

.Whe

nPy

thon

chec

ksfo

rg.

mem

ber,

itfir

stch

ecks

g's

vars

dict

iona

ryfo

r"m

embe

r,"th

en

1C

hapt

er10

onpa

ge99

Foo.

Ifw

ecr

eate

ane

wm

embe

rofg

,itw

illbe

adde

dto

g's

dict

iona

ry,b

utno

tFo

o's.

>>>

g.setx(5)

>>>

vars(g)

{'x':

5}

Not

eth

atif

we

now

assi

gna

valu

eto

g.y,

we

are

nota

ssig

ning

that

valu

eto

Foo.

y.Fo

o.y

will

still

be10

,but

g.y

will

now

over

ride

Foo.

y

>>>

g.y

=9

>>>

vars(g)

{'y':

9,

'x':

5}

>>>

vars(Foo)

{'y':

10,

'bar':

<function

bar

at

0x4d6a3c>,

'__module__':

'__main__',

'setx':

<function

setx

at

0x4d6a04>,

'__doc__':

None}

Sure

enou

gh,i

fwe

chec

kth

eva

lues

:

>>>

g.y

9 >>>

Foo.y

10 Not

eth

atf.y

will

also

be10

,as

Pyth

onw

on't

find

'y'i

nva

rs(f

),so

itw

illge

tth

eva

lue

of'y

'fro

mva

rs(F

oo).

Som

em

ayha

veal

sono

ticed

that

the

met

hods

inFo

oap

pear

inth

ecl

ass

dict

iona

ryal

ong

with

the

xan

dy.

Ifyo

ure

mem

berf

rom

the

sect

ion

onla

mbd

afo

rms2 ,

we

can

trea

tfu

nctio

nsju

stlik

eva

riab

les.

Thi

sm

eans

that

we

can

assi

gnm

etho

dsto

acl

assd

urin

gru

ntim

ein

the

sam

ew

ayw

eas

sign

edva

riabl

es.

Ifyo

udo

this

,tho

ugh,

rem

embe

rtha

tifw

eca

lla

met

hod

ofa

clas

sin

stan

ce,

the

first

para

met

erpa

ssed

toth

em

etho

dw

illal

way

sbe

the

clas

sin

stan

ceits

elf.

Cha

ngin

gC

lass

Dic

tiona

ries

2C

hapt

er14

.0.5

onpa

ge14

8

We

can

also

acce

ssth

em

embe

rsdi

ctio

nary

ofa

clas

sus

ing

the

__di

ct__

-m

embe

roft

hecl

ass.

>>>

g.__dict__

{'y':

9,

'x':

5}

Ifw

ead

d,re

mov

e,or

chan

geke

y-va

lue

pair

sfr

omg.

__di

ct__

,thi

sha

sth

esa

me

effe

ctas

ifw

eha

dm

ade

thos

ech

ange

sto

the

mem

bers

ofg.

>>>

g.__dict__['z']

=-4

>>>

g.z

-4 19

.0.4

New

Styl

eC

lass

es

New

styl

ecl

asse

sw

ere

intr

oduc

edin

pyth

on2.

2.A

new

-sty

lecl

ass

isa

clas

sth

atha

sa

built

-in

asits

base

,mos

tcom

mon

lyob

ject

.Ata

low

leve

l,a

maj

ordi

ffer

ence

betw

een

old

and

new

clas

ses

isth

eirt

ype.

Old

clas

sin

stan

ces

wer

e

allo

ftyp

einstance

.New

styl

ecl

ass

inst

ance

sw

illre

turn

the

sam

eth

ing

asx.

__cl

ass_

_for

thei

rtyp

e.T

his

puts

user

defin

edcl

asse

son

ale

velp

layi

ngfie

ldw

ithbu

ilt-i

ns.

Old

/Cla

ssic

clas

ses

are

slat

edto

disa

ppea

rin

Pyth

on3.

With

this

inm

ind

alld

evel

opm

ents

houl

dus

ene

wst

yle

clas

ses.

New

Styl

ecl

asse

sal

soad

dco

nstr

ucts

like

prop

ertie

san

dst

atic

met

hods

fam

iliar

toJa

vapr

ogra

mm

ers.

Old

/Cla

ssic

Cla

ss

>>>

classClassicFoo:

...

def__init__(self):

...

pass

New

Styl

eC

lass

>>>

classNewStyleFoo(object):

...

def__init__(self):

...

pass

Prop

ertie

s

Prop

ertie

sar

eat

trib

utes

with

gette

rand

sette

rmet

hods

.

>>>

classSpamWithProperties(object):

...

def__init__(self):

...

self.__egg

="MyEgg"

...

defget_egg(self):

...

return

self.__egg

...

defset_egg(self,

egg):

...

self.__egg

=egg

...

egg

=property(get_egg,

set_egg)

>>>

sp

=SpamWithProperties()

>>>

sp.egg

'MyEgg'

>>>

sp.egg

="Eggs

With

Spam"

>>>

sp.egg

'Eggs

With

Spam'

>>>

and

sinc

ePy

thon

2.6,

with

@pr

oper

tyde

cora

tor

>>>

classSpamWithProperties(object):

...

def__init__(self):

...

self.__egg

="MyEgg"

...

@property

...

defegg(self):

...

return

self.__egg

...

@egg.setter

...

defegg(self,

egg):

...

self.__egg

=egg

Stat

icM

etho

ds

Stat

icm

etho

dsin

Pyth

onar

eju

stlik

eth

eirc

ount

erpa

rts

inC

++or

Java

.Sta

ticm

etho

dsha

veno

"sel

f"ar

gum

enta

nddo

n'tr

equi

reyo

uto

inst

antia

teth

ecl

ass

befo

reus

ing

them

.The

yca

nbe

defin

edus

ing

stat

icm

etho

d()

>>>

classStaticSpam(object):

...

defStaticNoSpam():

...

print

"You

can't

have

have

the

spam,

spam,

eggs

and

spam

without

any

spam...

that's

disgusting"

...

NoSpam

=staticmethod(StaticNoSpam)

>>>

StaticSpam.NoSpam()

'You

can\'t

have

have

the

spam,

spam,

eggs

and

spam

without

any

spam...

that\'s

disgusting'

The

yca

nal

sobe

defin

edus

ing

the

func

tion

deco

rato

r@st

atic

met

hod.

>>>

classStaticSpam(object):

...

@staticmethod

...

defStaticNoSpam():

...

print

"You

can't

have

have

the

spam,

spam,

eggs

and

spam

without

any

spam...

that's

disgusting"

19.0

.5In

heri

tanc

e

Like

allo

bjec

torie

nted

lang

uage

s,Py

thon

prov

ides

fori

nher

itanc

e.In

herit

ance

isa

sim

ple

conc

eptb

yw

hich

acl

ass

can

exte

ndth

efa

cilit

ies

ofan

othe

rcla

ss,

orin

Pyth

on's

case

,mul

tiple

othe

rcla

sses

.Use

the

follo

win

gfo

rmat

fort

his:

class

ClassName(superclass1,superclass2,superclass3,...):

...

The

subc

lass

will

then

have

allt

hem

embe

rsof

itssu

perc

lass

es.I

fam

etho

dis

defin

edin

the

subc

lass

and

inth

esu

perc

lass

,the

mem

ber

inth

esu

bcla

ssw

illov

erri

deth

eon

ein

the

supe

rcla

ss.I

nor

dert

ous

eth

em

etho

dde

fined

inth

esu

perc

lass

,iti

sne

cess

ary

toca

llth

em

etho

das

anat

tribu

teon

the

defin

ing

clas

s,as

inFo

o.se

tx(f

,5)a

bove

:

>>>

classFoo:

...

defbar(self):

...

print

"I'm

doing

Foo.bar()"

...

x=

10

...

>>>

classBar(Foo):

...

defbar(self):

...

print

"I'm

doing

Bar.bar()"

...

Foo.bar(self)

...

y=

9...

>>>

g=

Bar()

>>>

Bar.bar(g)

I'm

doing

Bar.bar()

I'm

doing

Foo.bar()

>>>

g.y

9 >>>

g.x

10 Onc

eag

ain,

we

can

see

wha

t'sgo

ing

onun

dert

heho

odby

look

ing

atth

ecl

ass

dict

iona

ries

.

>>>

vars(g)

{}>>>

vars(Bar)

{'y':

9,

'__module__':

'__main__',

'bar':

<function

bar

at

0x4d6a04>,

'__doc__':

None}

>>>

vars(Foo)

{'x':

10,

'__module__':

'__main__',

'bar':

<function

bar

at

0x4d6994>,

'__doc__':

None}

Whe

nw

eca

llg.

x,it

first

look

sin

the

vars

(g)

dict

iona

ry,a

sus

ual.

Als

oas

abov

e,it

chec

ksva

rs(B

ar)n

ext,

sinc

eg

isan

inst

ance

ofB

ar.H

owev

er,t

hank

sto

inhe

rita

nce,

Pyth

onw

illch

eck

vars

(Foo

)ifi

tdoe

sn't

find

xin

vars

(Bar

).

19.0

.6Sp

ecia

lMet

hods

The

rear

ea

num

ber

ofm

etho

dsw

hich

have

rese

rved

nam

esw

hich

are

used

fors

peci

alpu

rpos

eslik

em

imic

king

num

eric

alor

cont

aine

rope

ratio

ns,a

mon

got

her

thin

gs.

All

ofth

ese

nam

esbe

gin

and

end

with

two

unde

rsco

res.

Itis

conv

entio

nth

atm

etho

dsbe

ginn

ing

with

asi

ngle

unde

rsco

rear

e'p

rivat

e'to

the

scop

eth

eyar

ein

trod

uced

with

in.

Initi

aliz

atio

nan

dD

elet

ion

__in

it__

One

ofth

ese

purp

oses

isco

nstr

uctin

gan

inst

ance

,and

the

spec

ialn

ame

for

this

is'_

_ini

t__'

.__

init_

_()

isca

lled

befo

rean

inst

ance

isre

turn

ed(i

tis

not

nece

ssar

yto

retu

rnth

ein

stan

cem

anua

lly).

As

anex

ampl

e,

class

A:

def__init__(self):

print'A.__init__()'

a=

A()

outp

uts

A.__init__()

__in

it__(

)can

take

argu

men

ts,i

nw

hich

case

itis

nece

ssar

yto

pass

argu

men

tsto

the

clas

sin

orde

rto

crea

tean

inst

ance

.For

exam

ple,

class

Foo:

def__init__

(self,

printme):

printprintme

foo

=Foo('Hi!')

outp

uts

Hi!

Her

eis

anex

ampl

esh

owin

gth

edi

ffer

ence

betw

een

usin

g__

init_

_()a

ndno

tus

ing

__in

it__(

):

class

Foo:

def__init__

(self,

x):

printx

foo

=Foo('Hi!')

class

Foo2:

defsetx(self,

x):

printx

f=

Foo2()

Foo2.setx(f,'Hi!')

outp

uts

Hi!

Hi!

__de

l__

Sim

ilarl

y,'_

_del

__'i

sca

lled

whe

nan

inst

ance

isde

stro

yed;

e.g.

whe

nit

isno

long

erre

fere

nced

.

Rep

rese

ntat

ion

__st

r__

Con

vert

ing

anob

ject

toa

stri

ng,a

sw

ithth

epr

ints

tate

men

torw

ithth

est

r()c

onve

rsio

nfu

nctio

n,ca

nbe

over

ridd

enby

over

ridi

ng__

str_

_.U

sual

ly,_

_str

__re

turn

sa

form

atte

dve

rsio

nof

the

obje

cts

cont

ent.

Thi

sw

illN

OT

usua

llybe

som

ethi

ngth

atca

nbe

exec

uted

.Fo

rexa

mpl

e:

classBar:

def__init__

(self,

iamthis):

self.iamthis

=iamthis

def__str__

(self):

return

self.iamthis

bar

=Bar('apple')

printbar

outp

uts

appl

e

__re

pr__

Thi

sfu

nctio

nis

muc

hlik

e__

str_

-_(

).If

__st

r__i

sno

tpre

sent

but

this

one

is,t

his

func

tion'

sou

tput

isus

edin

stea

dfo

rpri

ntin

g.__

repr

_-_i

sus

edto

retu

rna

repr

esen

tatio

nof

the

obje

ctin

stri

ngfo

rm.I

nge

nera

l,it

can

beex

ecut

edto

get

back

the

orig

inal

obje

ct.

Fore

xam

ple:

classBar:

def__init__

(self,

iamthis):

self.iamthis

=iamthis

def__repr__(self):

return

"Bar('%s')"

%self.iamthis

bar

=Bar('apple')

bar

outp

uts

(not

eth

edi

ffer

ence

:now

isno

tnec

essa

ryto

puti

tins

ide

apr

int)

Bar

('app

le')

Stri

ngR

epre

sent

atio

nO

ver-

ride

Func

tions

Func

tion

Ope

rato

r__

str_

_st

r(A

)__

repr

__re

pr(A

)__

unic

ode_

_un

icod

e(x)

(2.x

only

)

Att

ribu

tes

__se

tatt

r__

Thi

sis

the

func

tion

whi

chis

inch

arge

ofse

tting

attr

ibut

esof

acl

ass.

Itis

prov

ided

with

the

nam

ean

dva

lue

ofth

eva

riab

les

bein

gas

sign

ed.E

ach

clas

s,of

cour

se,

com

esw

itha

defa

ult_

_set

attr

__-

whi

chsi

mpl

yse

tsth

eva

lue

ofth

eva

riab

le,b

utw

eca

nov

erri

deit.

>>>classUnchangable:

...

def__setattr__(self,

name,

value):

...

print

"Nice

try"

...

>>>

u=

Unchangable()

>>>

u.x

=9

Nicetry

>>>

u.x

Trac

ebac

k(m

ostr

ecen

tcal

llas

t):

File

"<st

din>

",lin

e1,

in?

Attr

ibu-

teE

rror

:Unc

hang

able

inst

ance

has

noat

trib

ute

'x'

__ge

tatt

r___

Sim

ilart

o__

seta

ttr__

,exc

eptt

his

func

tion

isca

lled

whe

nw

etr

yto

acce

ssa

clas

sm

embe

r,an

dth

ede

faul

tsim

ply

retu

rns

the

valu

e.

>>>classHiddenMembers:

...

def

__getattr__(self,

name):

...

return"You

don't

get

to

see

"+

name

...

>>>

h=

HiddenMembers()

>>>

h.anything

"You

don't

get

to

see

anything"

__de

latt

r__

Thi

sfu

nctio

nis

calle

dto

dele

tean

attr

ibut

e.

>>>classPermanent:

...

def

__delattr__(self,

name):

...

printname,

"cannot

be

deleted"

...

>>>

p=

Permanent()

>>>

p.x

=9

>>>delp.x

xcannot

be

deleted

>>>

p.x

9

Att

ribu

teO

verr

ide

Func

tions

Func

tion

Indi

rect

form

Dir

ect

Form

__-

geta

ttr__

geta

ttr(A

,B

)A

.B

__-

seta

ttr__

seta

ttr(A

,B

,C)

A.B

=C

__-

dela

ttr__

dela

ttr(A

,B

)de

lA.B

Ope

rato

rO

verl

oadi

ng

Ope

rato

rove

rload

ing

allo

ws

usto

use

the

built

-inPy

thon

synt

axan

dop

erat

ors

toca

llfu

nctio

nsw

hich

we

defin

e.

Bin

ary

Ope

rato

rs

3C

hapt

er12

.6on

page

122

4C

hapt

er12

.6on

page

122

Ifa

clas

sha

sth

e__

add_

_fun

ctio

n,w

eca

nus

eth

e'+

'ope

rato

rto

add

inst

ance

sof

the

clas

s.T

his

will

call

__ad

d__w

ithth

etw

oin

stan

ces

ofth

ecl

ass

pass

edas

para

met

ers,

and

the

retu

rnva

lue

will

beth

ere

sult

ofth

ead

ditio

n.

>>>classFakeNumber:

...

n=

5...

def

__add__(A,B):

...

returnA.n

+B.n

...

>>>

c=

FakeNumber()

>>>

d=

FakeNumber()

>>>

d.n

=7

>>>

c+

d12 To

over

ride

the

augm

ente

das

sign

-m

ent3

oper

ator

s,m

erel

yad

d'i'

infr

onto

fthe

norm

albi

nary

oper

ator

,i.e

.for

'+='

use

'__i

add_

_'in

stea

dof

'__a

dd__

'.T

hefu

nctio

nw

illbe

give

non

ear

gum

ent,

whi

chw

illbe

the

obje

cton

the

righ

tsid

eof

the

augm

ente

das

sign

men

tope

rato

r.T

here

turn

edva

lue

ofth

efu

nctio

nw

illth

enbe

assi

gned

toth

eob

ject

onth

ele

ftof

the

oper

ator

.

>>>

c.__imul__

=lambdaB:

B.n

-6

>>>

c*=

d>>>

c1 It

isim

port

antt

ono

teth

atth

eau

g-m

ente

das

sign

men

t4op

erat

ors

will

also

use

the

norm

alop

erat

orfu

nc-

tions

ifth

eau

gmen

ted

oper

ator

func

tion

hasn

'tbe

ense

tdir

ectly

.T

his

will

wor

kas

expe

cted

,with

"__a

dd__

"be

ing

calle

dfo

r"+=

"an

dso

on.

>>>

c=

FakeNumber()

>>>

c+=

d>>>

c12

Bin

ary

Ope

rato

rO

verr

ide

Func

tions

Func

tion

Ope

rato

r__

add_

_A

+B

__su

b__

A-B

__m

ul__

A*

B__

true

div_

_A

/B__

floor

div_

_A

//B

__m

od__

A%

B__

pow

__A

**B

__an

d__

A&

B__

or__

A|B

__xo

r__

AˆB

__eq

__A

==B

__ne

__A

!=B

__gt

__A

>B

__lt_

_A

<B

__ge

__A

>=B

__le

__A

<=B

__ls

hift

__A

<<B

__rs

hift

__A

>>B

__co

ntai

ns__

Ain

BA

noti

nB

Una

ryO

pera

tors

Una

ryop

erat

ors

will

bepa

ssed

sim

ply

the

inst

ance

ofth

ecl

ass

that

they

are

calle

don

.

>>>

FakeNumber.__neg__

=lambda

A:

A.n

+6

>>>

-d

13

Una

ryO

pera

tor

Ove

rrid

eFu

nctio

nsFu

nctio

nO

pera

tor

__po

s__

+A__

neg_

_-A

__in

v__

˜A__

abs_

_ab

s(A

)__

len_

_le

n(A

)

Item

Ope

rato

rs

Itis

also

poss

ible

inPy

thon

toov

erri

deth

ein

dexi

ngan

dsl

icin

g5

oper

ator

s.T

his

allo

ws

usto

use

the

clas

s[i]

and

clas

s[a:

b]sy

ntax

onou

row

nob

ject

s.T

hesi

mpl

estf

orm

ofite

mop

erat

oris

__ge

titem

__.T

his

take

sas

apa

ram

eter

the

inst

ance

ofth

ecl

ass,

then

the

valu

eof

the

inde

x.

>>>classFakeList:

...

def

__getitem__(self,index):

...

returnindex*

2...

>>>

f=

FakeList()

>>>

f['a']

'aa'

We

can

also

defin

ea

func

tion

for

the

synt

axas

soci

ated

with

assi

gn-

ing

ava

lue

toan

item

.The

para

m-

eter

sfo

rthi

sfu

nctio

nin

clud

eth

eva

lue

bein

gas

sign

ed,i

nad

ditio

nto

the

para

met

ers

from

__ge

titem

__

>>>classFakeList:

...

def

__setitem__(self,index,value):

...

self.string

=index

+"

is

now

"+

value

...

>>>

f=

FakeList()

>>>

f['a']

='gone'

>>>

f.string

'a

is

now

gone'

We

can

doth

esa

me

thin

gw

ithsl

ices

.Onc

eag

ain,

each

synt

axha

sa

diff

eren

tpar

amet

erlis

tass

oci-

ated

with

it.

>>>classFakeList:

...

def

__getslice___(self,start,end):

...

returnstr(start)

+"

to

"+

str(end)

...

>>>

f=

FakeList()

>>>

f[1:4]

'1

to

4'

Kee

pin

min

dth

aton

eor

both

ofth

est

arta

nden

dpa

ram

eter

sca

nbe

blan

kin

slic

esy

ntax

.Her

e,Py

thon

has

defa

ultv

alue

forb

oth

the

star

tan

dth

een

d,as

show

belo

w.

>>

f[:]

'0

to

2147483647'

Not

eth

atth

ede

faul

tval

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rthe

end

ofth

esl

ice

show

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reis

sim

-pl

yth

ela

rges

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pend

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Cco

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ler.

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sets

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)•

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ote

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nctio

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[i]

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[i]=

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5C

hapt

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Oth

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divm

od__

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float

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hex_

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ath.

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+)

19.0

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ogra

mm

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Prac

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The

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pyth

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For

the

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ition

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6http://en.wikibooks.org/wiki/C%2B%2B%20Programming%

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Enc

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Sinc

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ssit.

Whe

nus

ing

part

sof

acl

ass

orm

odul

eot

hert

han

the

inte

nded

inte

rfac

e,ke

epin

min

dth

atth

eth

ose

parts

may

chan

gein

late

rver

sion

sof

the

mod

ule,

and

you

may

even

caus

eer

rors

orun

defin

edbe

havi

ors

inth

em

odul

e.

8http://en.wikipedia.org/wiki/Information%20Hiding

Doc

Stri

ngs

Whe

nde

finin

ga

clas

s,it

isco

nven

tion

todo

cum

entt

hecl

ass

usin

ga

stri

nglit

eral

atth

est

arto

fthe

clas

sde

finiti

on.T

his

stri

ngw

illth

enbe

plac

edin

the

__do

c__a

ttrib

ute

ofth

ecl

ass

defin

ition

.

>>>

classDocumented:

...

"""This

is

adocstring"""

...

defexplode(self):

...

"""

...

This

method

is

documented,

too!

The

coder

is

really

serious

about

...

making

this

class

usable

by

others

who

don't

know

the

code

as

well

...

as

he

does.

...

...

"""

...

print

"boom"

>>>

d=

Documented()

>>>

d.__doc__

'This

is

adocstring'

Doc

stri

ngs

are

ave

ryus

eful

way

todo

cum

enty

ourc

ode.

Eve

nif

you

neve

rw

rite

asi

ngle

piec

eof

sepa

rate

docu

men

tatio

n(a

ndle

t'sad

mit

it,do

ing

sois

the

low

estp

rior

ityfo

rman

yco

ders

),in

clud

ing

info

rmat

ive

docs

trin

gsin

your

clas

ses

will

goa

long

way

tow

ard

mak

ing

them

usab

le.

Seve

ralt

ools

exis

tfor

turn

ing

the

docs

tring

sin

Pyth

onco

dein

tore

adab

leA

PIdo

cum

enta

tion,

e.g.

,E

pyD

oc9 .

Don

'tju

stst

opat

docu

men

ting

the

clas

sde

finiti

on,e

ither

.Eac

hm

etho

din

the

clas

ssh

ould

have

itsow

ndo

cstr

ing

asw

ell.

Not

eth

atth

edo

cstr

ing

for

the

met

hod

expl

ode

inth

eex

ampl

ecl

ass

Doc

umen

ted

abov

eha

sa

fair

lyle

ngth

ydo

cstri

ngth

atsp

ans

seve

rall

ines

.Its

form

attin

gis

inac

cord

ance

with

the

styl

esu

gges

tions

ofPy

thon

'scr

eato

r,G

uido

van

Ros

sum

.

9http://epydoc.sourceforge.net/using.html

Add

ing

met

hods

atru

ntim

e

Toa

clas

s

Itis

fairl

yea

syto

add

met

hods

toa

clas

sat

runt

ime.

Lets

assu

me

that

we

have

acl

ass

calle

dSp

aman

da

func

tion

cook

.We

wan

tto

beab

leto

use

the

func

tion

cook

onal

lins

tanc

esof

the

clas

sSp

am:

class

Spam:

def__init__(self):

self.myeggs

=5

def

cook(self):

print"cooking

%s

eggs"

%self.myeggs

Spam.cook

=cook

#add

the

function

to

the

class

Spam

eggs

=Spam()

#NOW

create

anew

instance

of

Spam

eggs.cook()

#and

we

are

ready

to

cook!

Thi

sw

illou

tput

cooking

5eggs

Toan

inst

ance

ofa

clas

s

Itis

abi

tmor

etr

icky

toad

dm

etho

dsto

anin

stan

ceof

acl

ass

that

has

alre

ady

been

crea

ted.

Lets

assu

me

agai

nth

atw

eha

vea

clas

sca

lled

Spam

and

we

have

alre

ady

crea

ted

eggs

.But

then

we

notic

eth

atw

ew

ante

dto

cook

thos

eeg

gs,

butw

edo

notw

antt

ocr

eate

ane

win

stan

cebu

trat

heru

seth

eal

read

ycr

eate

don

e:

class

Spam:

def__init__(self):

self.myeggs

=5

eggs

=Spam()

def

cook(self):

print"cooking

%s

eggs"

%self.myeggs

import

types

f=

types.MethodType(cook,

eggs,

Spam)

eggs.cook

=f

eggs.cook()

Now

we

can

cook

oure

ggs

and

the

last

stat

emen

twill

outp

ut:

cooking

5eggs

Usi

nga

func

tion

We

can

also

wri

tea

func

tion

that

will

mak

eth

epr

oces

sof

addi

ngm

etho

dsto

anin

stan

ceof

acl

ass

easi

er.

def

attach_method(fxn,

instance,

myclass):

f=

types.MethodType(fxn,

instance,

myclass)

setattr(instance,

fxn.__name__,

f)

All

we

now

need

todo

isca

llth

eat

tach

_met

hod

with

the

argu

men

tsof

the

func

tion

we

wan

tto

atta

ch,t

hein

stan

cew

ew

antt

oat

tach

itto

and

the

clas

sth

ein

stan

ceis

deriv

edfr

om.T

hus

ourf

unct

ion

call

mig

htlo

oklik

eth

is:

attach_method(cook,

eggs,

Spam)

Not

eth

atin

the

func

tion

add_

met

hod

we

cann

otw

riteinstance.fxn=

fsi

nce

this

wou

ldad

da

func

tion

calle

dfx

nto

the

inst

ance

.

fr:P

rogr

amm

atio

nPy

thon

/Pro

gram

mat

ion

orie

nté

obje

t10pt

:Pyt

hon/

Con

ceito

sbá

sico

s/C

lass

es11

10http://fr.wikibooks.org/wiki/Programmation%20Python%

2FProgrammation%20orient%E9%20objet

11http://pt.wikibooks.org/wiki/Python%2FConceitos%20b%

E1sicos%2FClasses

20M

etaC

lass

es

Inpy

thon

,cla

sses

are

them

selv

esob

ject

s.Ju

stas

othe

robj

ects

are

inst

ance

sof

apa

rtic

ular

clas

s,cl

asse

sth

emse

lves

are

inst

ance

sof

am

etac

lass

.

20.0

.8C

lass

Fact

orie

s

The

sim

ples

tuse

ofpy

thon

met

acla

sses

isa

clas

sfa

ctor

y.T

his

conc

eptm

akes

use

ofth

efa

ctth

atcl

ass

defin

ition

sin

pyth

onar

efir

st-c

lass

obje

cts1 .

Such

a

1http://en.wikipedia.org/wiki/First-class%20%28object%29

227

func

tion

can

crea

teor

mod

ify

acl

ass

defin

ition

,usi

ngth

esa

me

synt

ax2

one

wou

ldno

rmal

lyus

ein

decl

arin

ga

clas

sde

finiti

on.

Onc

eag

ain,

itis

usef

ulto

use

the

mod

elof

clas

ses

asdi

ctio

nari

es3 .

Firs

t,le

t'slo

okat

aba

sic

clas

sfa

ctor

y:

>>>

defStringContainer():

...

#define

aclass

...

classString:

...

content_string

=""

...

deflen(self):

...

return

len(self.content_string)

...

#return

the

class

definition

...

returnString

...

>>>

#create

the

class

definition

...

container_class

=StringContainer()

>>>

>>>

#create

an

instance

of

the

class

...

wrapped_string

=container_class()

>>>

2C

hapt

er19

.0.1

onpa

ge18

93

Cha

pter

19.0

.3on

page

194

>>>

#take

it

for

atest

drive

...

wrapped_string.content_string

='emu

emissary'

>>>

wrapped_string.len()

12 Of

cour

se,

just

like

any

othe

rda

tain

pyth

on,

clas

sde

finiti

ons

can

also

bem

odifi

ed.A

nym

odifi

catio

nsto

attr

ibut

esin

acl

ass

defin

ition

will

bese

enin

any

inst

ance

sof

that

defin

ition

,so

long

asth

atin

stan

ceha

sn't

over

ridd

enth

eat

trib

ute

that

you'

rem

odif

ying

.

>>>

defDeAbbreviate(sequence_container):

...

sequence_container.length

=sequence_container.len

...

delsequence_container.len

...

>>>

DeAbbreviate(container_class)

>>>

wrapped_string.length()

12>>>

wrapped_string.len()

Traceback

(most

recent

call

last):

File

"<stdin>",

line

1,

in

?AttributeError:

String

instance

has

no

attribute

'len'

You

can

also

dele

tecl

ass

defin

ition

s,bu

ttha

twill

nota

ffec

tins

tanc

esof

the

clas

s. >>>

del

container_class

>>>

wrapped_string2

=container_class()

Traceback

(most

recent

call

last):

File

"<stdin>",

line

1,

in

?NameError:

name

'container_class'

is

not

defined

>>>

wrapped_string.length()

12

20.0

.9T

hety

peM

etac

lass

The

met

acla

ssfo

rall

stan

dard

pyth

onty

pes

isth

e"t

ype"

obje

ct.

>>>

type(object)

<type

'type'>

>>>

type(int)

<type

'type'>

>>>

type(list)

<type

'type'>

Just

like

list,

inta

ndob

ject

,"ty

pe"

isits

elfa

norm

alpy

thon

obje

ct,a

ndis

itsel

fan

inst

ance

ofa

clas

s.In

this

case

,iti

sin

fact

anin

stan

ceof

itsel

f.

>>>

type(type)

<type

'type'>

Itca

nbe

inst

antia

ted

tocr

eate

new

clas

sob

ject

ssi

mila

rly

toth

ecl

ass

fact

ory

exam

ple

abov

eby

pass

ing

the

nam

eof

the

new

clas

s,th

eba

secl

asse

sto

inhe

ritfr

om,a

nda

dict

iona

ryde

finin

gth

ena

mes

pace

tous

e.

Fori

nsta

nce,

the

code

:

>>>

classMyClass(BaseClass):

...

attribute

=42

Cou

ldal

sobe

wri

tten

as:

>>>

MyClass

=type("MyClass",

(BaseClass,),

{'attribute'

:42})

20.0

.10

Met

acla

sses

Itis

poss

ible

tocr

eate

acl

ass

with

adi

ffer

entm

etac

lass

than

type

byse

tting

its__

met

acla

ss__

attr

ibut

ew

hen

defin

ing.

Whe

nth

isis

done

,the

clas

s,an

dits

subc

lass

will

becr

eate

dus

ing

your

cust

omm

etac

lass

.For

exam

ple

class

CustomMetaclass(type):

def__init__(cls,

name,

bases,

dct):

print"Creating

class

%s

using

CustomMetaclass"

%name

super(CustomMetaclass,

cls).__init__(name,

bases,

dct)

class

BaseClass(object):

__metaclass__

=CustomMetaclass

class

Subclass1(BaseClass):

pass

Thi

sw

illpr

int

Creating

class

BaseClass

using

CustomMetaclass

Creating

class

Subclass1

using

CustomMetaclass

By

crea

ting

acu

stom

met

acla

ssin

this

way

,it

ispo

ssib

leto

chan

geho

wth

ecl

ass

isco

nstr

ucte

d.T

his

allo

ws

you

toad

dor

rem

ove

attr

ibut

esan

dm

etho

ds,r

egis

terc

reat

ion

ofcl

asse

san

dsu

bcla

sses

crea

tion

and

vari

ous

othe

rm

anip

ulat

ions

whe

nth

ecl

ass

iscr

eate

d.

20.0

.11

Mor

ere

sour

ces

•W

ikip

edia

artic

leon

Asp

ectO

rien

ted

Prog

ram

min

g4

•U

nify

ing

type

san

dcl

asse

sin

Pyth

on2.

25

4http://en.wikipedia.org/wiki/Aspect-oriented_programming

5http://www.python.org/2.2/descrintro.html

•O

'Rei

llyA

rtic

leon

Pyth

onM

etac

lass

es6

6http://www.onlamp.com/pub/a/python/2003/04/17/metaclasses.

html

21R

egul

arE

xpre

ssio

n

Pyth

onin

clud

esa

mod

ule

forw

orki

ngw

ithre

gula

rexp

ress

ions

onst

rings

.For

mor

ein

form

atio

nab

outw

ritin

gre

gula

rexp

ress

ions

and

synt

axno

tspe

cific

toPy

thon

,see

the

regu

lar

expr

essi

ons1

wik

iboo

k.Py

thon

'sre

gula

rex

pres

sion

synt

axis

sim

ilart

oPe

rl's2

Tost

artu

sing

regu

lare

xpre

ssio

nsin

your

Pyth

onsc

ript

s,ju

stim

port

the

"re"

mod

ule:

1http://en.wikibooks.org/wiki/regular%20expressions

2http://en.wikibooks.org/wiki/Perl%20Programming%2FRegular%

20Expressions%20Reference

235

import

re

21.1

Patt

ern

obje

cts

Ifyo

u're

goin

gto

beus

ing

the

sam

ere

gexp

mor

eth

anon

cein

apr

ogra

m,o

rif

you

just

wan

tto

keep

the

rege

xps

sepa

rate

dso

meh

ow,y

oush

ould

crea

tea

patte

rnob

ject

,and

refe

rto

itla

terw

hen

sear

chin

g/re

plac

ing.

Tocr

eate

apa

ttern

obje

ct,u

seth

eco

mpi

lefu

nctio

n.

import

re

foo

=re.compile(r'foo(.{,5})bar',

re.I+re.S)

The

first

argu

men

tis

the

patte

rn,w

hich

mat

ches

the

stri

ng"f

oo",

follo

wed

byup

to5

ofan

ych

arac

ter,

then

the

stri

ng"b

ar",

stor

ing

the

mid

dle

char

acte

rsto

agr

oup,

whi

chw

illbe

disc

usse

dla

ter.

The

seco

nd,o

ptio

nal,

argu

men

tis

the

flag

orfla

gsto

mod

ify

the

rege

xp's

beha

vior

.The

flags

them

selv

esar

esi

mpl

y

vari

able

sre

ferr

ing

toan

inte

ger

used

byth

ere

gula

rex

pres

sion

engi

ne.

Inot

herl

angu

ages

,the

sew

ould

beco

nsta

nts,

butP

ytho

ndo

esno

thav

eco

nsta

nts.

Som

eof

the

regu

lar

expr

essi

onfu

nctio

nsdo

not

supp

ort

addi

ngfla

gsas

apa

ram

eter

whe

nde

finin

gth

epa

ttern

dire

ctly

inth

efu

nctio

n,if

you

need

any

ofth

efla

gs,i

tis

best

tous

eth

eco

mpi

lefu

nctio

nto

crea

tea

patte

rnob

ject

.

The

rpr

eced

ing

the

expr

essi

onst

ring

indi

cate

sth

atit

shou

ldbe

trea

ted

asa

raw

stri

ng.

Thi

ssh

ould

norm

ally

beus

edw

hen

wri

ting

rege

xps,

soth

atba

cksl

ashe

sar

ein

terp

rete

dlit

eral

lyra

ther

than

havi

ngto

bees

cape

d.

The

diff

eren

tflag

sar

e:

Abb

revi

atio

nFu

llna

me

Des

crip

tion

re.I

re.IGNORECASE

Mak

esth

ere

gexp

case

-ins

ensi

tive3

3http://en.wikipedia.org/wiki/case%20sensitivity

Abb

revi

atio

nFu

llna

me

Des

crip

tion

re.L

re.LOCALE

Mak

esth

ebe

havi

orof

som

esp

ecia

lse-

quen

ces

(\w,\W,

\b,\B,\s,\S

)de

pend

ento

nth

ecu

r-re

ntlo

cale

4

re.M

re.MULTILINE

Mak

esth

eˆ

and$

char

acte

rsm

atch

atth

ebe

ginn

ing

and

end

ofea

chlin

e,ra

ther

than

just

the

begi

n-ni

ngan

den

dof

the

stri

ng

4http://en.wikipedia.org/wiki/locale

Abb

revi

atio

nFu

llna

me

Des

crip

tion

re.S

re.DOTALL

Mak

esth

e.

char

-ac

term

atch

ever

ych

arac

teri

nclu

ding

new

lines

.re.U

re.UNICODE

Mak

es\w,\W,

\b,\B,\d,\D,

\s,\S

depe

nden

ton

Uni

code

char

acte

rpr

oper

ties

Abb

revi

atio

nFu

llna

me

Des

crip

tion

re.X

re.VERBOSE

Igno

res

whi

tesp

ace

exce

ptw

hen

ina

char

acte

rcla

ssor

prec

eded

byan

non-

esca

ped

back

slas

h,an

dig

nore

s#

(exc

ept

whe

nin

ach

arac

ter

clas

sor

prec

eded

byan

non-

esca

ped

back

-sl

ash)

and

ever

ythi

ngaf

teri

tto

the

end

ofa

line,

soit

can

beus

edas

aco

mm

ent.

Thi

sal

low

sfo

rcle

aner

-lo

okin

gre

gexp

s.

21.2

Mat

chin

gan

dse

arch

ing

One

ofth

em

ostc

omm

onus

esfo

rreg

ular

expr

essi

ons

isex

trac

ting

apa

rtof

ast

ring

orte

stin

gfo

rthe

exis

tenc

eof

apa

ttern

ina

stri

ng.P

ytho

nof

fers

seve

ral

func

tions

todo

this

.

The

mat

chan

dse

arch

func

tions

dom

ostly

the

sam

eth

ing,

exce

ptth

atth

em

atch

func

tion

will

only

retu

rna

resu

ltif

the

patte

rnm

atch

esat

the

begi

nnin

gof

the

stri

ngbe

ing

sear

ched

,whi

lese

arch

will

find

am

atch

anyw

here

inth

est

ring

.

>>>

import

re

>>>

foo

=re.compile(r'foo(.{,5})bar',

re.I+re.S)

>>>

st1

='Foo,

Bar,

Baz'

>>>

st2

='2.

foo

is

bar'

>>>

search1

=foo.search(st1)

>>>

search2

=foo.search(st2)

>>>

match1

=foo.match(st1)

>>>

match2

=foo.match(st2)

Inth

isex

ampl

e,m

atch

2w

illbe

None

,bec

ause

the

stri

ngst2

does

nots

tart

with

the

give

npa

ttern

.The

othe

r3re

sults

will

beM

atch

obje

cts

(see

belo

w).

You

can

also

mat

chan

dse

arch

with

outc

ompi

ling

are

gexp

:

>>>

search3

=re.search('oo.*ba',

st1,

re.I)

Her

ew

eus

eth

ese

arch

func

tion

ofth

ere

mod

ule,

rath

erth

anof

the

patte

rnob

ject

.For

mos

tcas

es,i

tsbe

stto

com

pile

the

expr

essi

onfir

st.N

otal

loft

here

mod

ule

func

tions

supp

ortt

hefla

gsar

gum

enta

ndif

the

expr

essi

onis

used

mor

eth

anon

ce,c

ompi

ling

first

ism

ore

effic

ient

and

lead

sto

clea

nerl

ooki

ngco

de.

The

com

pile

dpa

ttern

obje

ctfu

nctio

nsal

soha

vepa

ram

eter

sfo

rsta

rtin

gan

den

ding

the

sear

ch,

tose

arch

ina

subs

trin

gof

the

give

nst

ring

.In

the

first

exam

ple

inth

isse

ctio

n,match2

retu

rns

nore

sult

beca

use

the

patte

rndo

esno

tsta

rtat

the

begi

nnin

gof

the

stri

ng,b

utif

we

do:

>>>

match3

=foo.match(st2,

3)

itw

orks

,be

caus

ew

ete

llit

tost

art

sear

chin

gat

char

acte

rnu

mbe

r3

inth

est

ring

.

Wha

tifw

ew

antt

ose

arch

form

ultip

lein

stan

ces

ofth

epa

ttern

?Th

enw

eha

vetw

oop

tions

.W

eca

nus

eth

est

arta

nden

dpo

sitio

npa

ram

eter

sof

the

sear

chan

dm

atch

func

tion

ina

loop

,get

ting

the

posi

tion

tost

arta

tfro

mth

epr

evio

usm

atch

obje

ct(s

eebe

low

)orw

eca

nus

eth

efin

dall

and

findi

terf

unct

ions

.The

finda

llfu

nctio

nre

turn

sa

listo

fmat

chin

gst

ring

s,us

eful

fors

impl

ese

arch

ing.

For

anyt

hing

slig

htly

com

plex

,th

efin

dite

rfu

nctio

nsh

ould

beus

ed.

Thi

sre

turn

san

itera

toro

bjec

t,th

atw

hen

used

ina

loop

,yie

lds

Mat

chob

ject

s.Fo

rex

ampl

e:

>>>

str3

='foo,

Bar

Foo.

BAR

FoO:

bar'

>>>

foo.findall(str3)

[',

',

'.

',

':

']

>>>

formatch

in

foo.finditer(str3):

...

match.group(1)

...

',

''.

'':

'

Ifyo

u're

goin

gto

beite

ratin

gov

erth

ere

sults

ofth

ese

arch

,usi

ngth

efin

dite

rfu

nctio

nis

alm

osta

lway

sa

bette

rcho

ice.

21.2

.1M

atch

obje

cts

Mat

chob

ject

sar

ere

turn

edby

the

sear

chan

dm

atch

func

tions

,and

incl

ude

info

rmat

ion

abou

tthe

patte

rnm

atch

.

The

grou

pfu

nctio

nre

turn

sa

strin

gco

rres

pond

ing

toa

capt

ure

grou

p(p

arto

fare

gexp

wra

pped

in()

)oft

heex

pres

sion

,ori

fno

grou

pnu

mbe

ris

give

n,th

een

tire

mat

ch.U

sing

thesearch1

vari

able

we

defin

edab

ove:

>>>

search1.group()

'Foo,

Bar'

>>>

search1.group(1)

',

'

Cap

ture

grou

psca

nal

sobe

give

nst

ring

nam

esus

ing

asp

ecia

lsyn

tax

and

refe

rred

toby

matchobj.group('name')

.For

sim

ple

expr

essi

ons

this

isun

nece

ssar

y,bu

tfor

mor

eco

mpl

exex

pres

sion

sit

can

beve

ryus

eful

.

You

can

also

gett

hepo

sitio

nof

am

atch

ora

grou

pin

ast

ring

,usi

ngth

est

art

and

end

func

tions

:

>>>

search1.start()

0 >>>

search1.end()

8 >>>

search1.start(1)

3 >>>

search1.end(1)

5 Thi

sre

turn

sth

est

arta

nden

dlo

catio

nsof

the

entir

em

atch

,and

the

star

tand

end

ofth

efir

st(a

ndin

this

case

only

)cap

ture

grou

p,re

spec

tivel

y.

21.3

Rep

laci

ng

Ano

ther

use

forr

egul

arex

pres

sion

sis

repl

acin

gte

xtin

ast

ring

.To

doth

isin

Pyth

on,u

seth

esu

bfu

nctio

n.

sub

take

sup

to3

argu

men

ts:

The

text

tore

plac

ew

ith,t

hete

xtto

repl

ace

in,

and,

optio

nally

,the

max

imum

num

ber

ofsu

bstit

utio

nsto

mak

e.U

nlik

eth

em

atch

ing

and

sear

chin

gfu

nctio

ns,s

ubre

turn

sa

stri

ng,c

onsi

stin

gof

the

give

nte

xtw

ithth

esu

bstit

utio

n(s)

mad

e.

>>>

import

re

>>>

mystring

='This

string

has

aq

in

it'

>>>

pattern

=re.compile(r'(a[n]?

)(\w)

')

>>>

newstring

=pattern.sub(r"\1'\2'

",

mystring)

>>>

newstring

"This

string

has

a'q'

in

it"

This

take

san

ysi

ngle

alph

anum

eric

char

acte

r(\w

inre

gula

rexp

ress

ion

synt

ax)

prec

eded

by"a

"or

"an"

and

wra

psin

insi

ngle

quot

es.T

he\1

and\2

inth

e

repl

acem

ents

tring

are

back

refe

renc

esto

the

2ca

ptur

egr

oups

inth

eex

pres

sion

;th

ese

wou

ldbe

grou

p(1)

and

grou

p(2)

ona

Mat

chob

ject

from

ase

arch

.

The

subn

func

tion

issi

mila

rto

sub,

exce

ptit

retu

rns

atu

ple,

cons

istin

gof

the

resu

ltst

ring

and

the

num

bero

frep

lace

men

tsm

ade.

Usi

ngth

est

ring

and

expr

essi

onfr

ombe

fore

:

>>>

subresult

=pattern.subn(r"\1'\2'

",

mystring)

>>>

subresult

("This

string

has

a'q'

in

it",

1)

21.4

Oth

erfu

nctio

ns

The

rem

odul

eha

sa

few

othe

rfun

ctio

nsin

addi

tion

toth

ose

disc

usse

dab

ove.

The

split

func

tion

split

sa

stri

ngba

sed

ona

give

nre

gula

rexp

ress

ion:

>>>

import

re

>>>

mystring

='1.

First

part

2.

Second

part

3.

Third

part'

>>>

re.split(r'\d\.',

mystring)

['',

'First

part

',

'Second

part

',

'Third

part']

The

esca

pefu

nctio

nes

cape

sal

lnon

-alp

hanu

mer

icch

arac

ters

ina

stri

ng.T

his

isus

eful

ifyo

une

edto

take

anun

know

nst

ring

that

may

cont

ain

rege

xpm

etac

hara

cter

slik

e(

and.

and

crea

tea

regu

lare

xpre

ssio

nfr

omit.

>>>

re.escape(r'This

text

(and

this)

must

be

escaped

with

a"\"

to

use

in

aregexp.')

'This\\

text\\

\\(and\\

this\\)\\

must\\

be\\

escaped\\

with\\

a\\

\\"\\\\\\"\\

to\\

use\\

in\\

a\\

regexp\\.'

21.5

Ext

erna

llin

ks

•Py

thonre

docu

men

tatio

n5-F

ulld

ocum

enta

tion

fort

here

mod

ule,

incl

udin

gpa

ttern

obje

cts

and

mat

chob

ject

s

5http://docs.python.org/library/re.html

fr:P

rogr

amm

atio

nPy

thon

/Reg

ex6

6http://fr.wikibooks.org/wiki/Programmation%20Python%

2FRegex

22G

UIP

rogr

amm

ing

The

rear

eva

riou

sG

UIt

oolk

itsto

star

twith

.

22.1

Tki

nter

Tkin

ter,

aPy

thon

wra

pper

for

Tcl/T

k1 ,com

esbu

ndle

dw

ithPy

thon

(atl

east

onW

in32

plat

form

thou

ghit

can

bein

stal

led

onU

nix/

Lin

uxan

dM

acm

achi

nes)

and

prov

ides

acr

oss-

plat

form

GU

I.It

isa

rela

tivel

ysi

mpl

eto

lear

nye

tpow

erfu

l

1http://en.wikibooks.org/wiki/Programming%3ATcl%20

251

tool

kitt

hatp

rovi

des

wha

tapp

ears

tobe

am

odes

tset

ofw

idge

ts.

How

ever

,be

caus

eth

eT

kint

erw

idge

tsar

eex

tens

ible

,man

yco

mpo

und

wid

gets

can

becr

eate

dra

ther

easi

ly(e

.g.c

ombo

-box

,scr

olle

dpa

nes)

.Bec

ause

ofits

mat

urity

and

exte

nsiv

edo

cum

enta

tion

Tki

nter

has

been

desi

gnat

edas

the

defa

cto

GU

Ifo

rPyt

hon.

Tocr

eate

ave

rysi

mpl

eT

kint

erw

indo

wfr

ame

one

only

need

sth

efo

llow

ing

lines

ofco

de:

import

Tkinter

root

=Tkinter.Tk()

root.mainloop()

From

anob

ject

-ori

ente

dpe

rspe

ctiv

eon

eca

ndo

the

follo

win

g:

import

Tkinter

class

App:

def__init__(self,

master):

button

=Tkinter.Button(master,

text="I'm

aButton.")

button.pack()

if

__name__==

'__main__':

root

=Tkinter.Tk()

app

=App(root)

root.mainloop()

Tole

arn

mor

eab

outT

kint

ervi

sitt

hefo

llow

ing

links

:

•ht

tp://

ww

w.a

stro

.was

hing

ton.

edu/

user

s/ro

wen

/Tki

nter

Sum

mar

y.ht

ml2

<-A

sum

mar

y

http

://in

foho

st.n

mt.e

du/tc

c/he

lp/la

ng/p

ytho

n/tk

inte

r.htm

l3<-

Atu

tori

al

•ht

tp://

ww

w.p

ytho

nwar

e.co

m/li

brar

y/tk

inte

r/in

trod

uctio

n/4

<-A

refe

renc

e

2http://www.astro.washington.edu/users/rowen/TkinterSummary.

html

3http://infohost.nmt.edu/tcc/help/lang/python/tkinter.html

4http://www.pythonware.com/library/tkinter/introduction/

22.2

PyG

TK

See

also

book

PyG

TKFo

rG

UIP

rogr

amm

ing5

PyG

TK

6pr

ovid

esa

conv

enie

ntw

rapp

erfo

rth

eG

TK

+7lib

rary

for

use

inPy

thon

prog

ram

s,ta

king

care

ofm

any

ofth

ebo

ring

deta

ilssu

chas

man

agin

gm

emor

yan

dty

peca

stin

g.T

heba

reG

TK

+to

olki

trun

son

Lin

ux,W

indo

ws,

and

Mac

OS

X(p

orti

npr

ogre

ss),

butt

hem

ore

exte

nsiv

efe

atur

es—

whe

nco

mbi

ned

with

PyO

RB

itan

dgn

ome-

pyth

on—

requ

ire

aG

NO

ME

8in

stal

l,an

dca

nbe

used

tow

rite

full

feat

ured

GN

OM

Eap

plic

atio

ns.

Hom

ePa

ge9

5http://en.wikibooks.org/wiki/PyGTK%20For%20GUI%

20Programming

6http://www.pygtk.org/

7http://www.gtk.org

8http://www.gnome.org

9http://www.pygtk.org/

22.3

PyQ

t

PyQ

tis

aw

rapp

erar

ound

the

cros

s-pl

atfo

rmQ

tC++

tool

kit10

.Ith

asm

any

wid

gets

and

supp

ort

clas

ses11

supp

ortin

gSQ

L,O

penG

L,S

VG

,XM

L,a

ndad

vanc

edgr

aphi

csca

pabi

litie

s.A

PyQ

thel

low

orld

exam

ple:

from

PyQt4.QtCore

import

*from

PyQt4.QtGui

import

*

class

App(QApplication):

def__init__(self,

argv):

super(App,

self).__init__(argv)

self.msg

=QLabel("Hello,

World!")

self.msg.show()

if

__name__==

"__main__":

import

sys

10http://www.trolltech.com/products/qt

11http://www.riverbankcomputing.com/Docs/PyQt4/html/classes.

html

app

=App(sys.argv)

sys.exit(app.exec_)

PyQ

t12is

ase

tofb

indi

ngs

fort

hecr

oss-

plat

form

Qt13

appl

icat

ion

fram

ewor

k.Py

Qtv

4su

ppor

tsQ

t4an

dPy

Qtv

3su

ppor

tsQ

t3an

dea

rlie

r.

22.4

wxP

ytho

n

Bin

ding

sfo

rthe

cros

spl

atfo

rmto

olki

tw

xWid

gets

14.W

xWid

gets

isav

aila

ble

onW

indo

ws,

Mac

into

sh,a

ndU

nix/

Lin

ux.

import

wx

class

test(wx.App):

def__init__(self):

12http://www.riverbankcomputing.co.uk/pyqt/

13http://en.wikibooks.org/wiki/Qt

14http://www.wxwidgets.org/

wx.App.__init__(self,

redirect=False)

defOnInit(self):

frame

=wx.Frame(None,

-1,

"Test",

pos=(50,50),

size=(100,40),

style=wx.DEFAULT_FRAME_STYLE)

button

=wx.Button(frame,

-1,

"Hello

World!",

(20,

20))

self.frame

=frame

self.frame.Show()

returnTrue

if

__name__==

'__main__':

app

=test()

app.MainLoop()

•w

xPyt

hon15

15http://wxpython.org/

22.5

Dab

o

Dab

ois

afu

ll3-

tiera

pplic

atio

nfr

amew

ork.

Its

UIl

ayer

wra

psw

xPyt

hon,

and

grea

tlysi

mpl

ifies

the

synt

ax.

import

dabo

dabo.ui.loadUI("wx")

class

TestForm(dabo.ui.dForm):

defafterInit(self):

self.Caption

="Test"

self.Position

=(50,

50)

self.Size

=(100,

40)

self.btn

=dabo.ui.dButton(self,

Caption="Hello

World",

OnHit=self.onButtonClick)

self.Sizer.append(self.btn,

halign="center",

border=20)

defonButtonClick(self,

evt):

dabo.ui.info("Hello

World!")

if

__name__==

'__main__':

app

=dabo.ui.dApp()

app.MainFormClass

=TestForm

app.start()

•D

abo16

22.6

pyFl

tk

pyFl

tk17

isa

Pyth

onw

rapp

erfo

rth

eFL

TK

18,a

light

wei

ghtc

ross

-pla

tfor

mG

UIt

oolk

it.It

isve

rysi

mpl

eto

lear

nan

dal

low

sfo

rcom

pact

user

inte

rfac

es.

The

"Hel

loW

orld

"ex

ampl

ein

pyFl

tklo

oks

like:

from

fltk

import

*

window

=Fl_Window(100,

100,

200,

90)

16http://dabodev.com/

17http://pyfltk.sourceforge.net/

18http://www.fltk.org/

button

=Fl_Button(9,20,180,50)

button.label("Hello

World")

window.end()

window.show()

Fl.run()

22.7

Oth

erTo

olki

ts

•Py

KD

E19

-Par

toft

hekd

ebin

ding

spa

ckag

e,it

prov

ides

apy

thon

wra

pper

fort

heK

DE

libra

ries

.•

PyX

PCO

M20

prov

ides

aw

rapp

erar

ound

the

Moz

illa

XPC

OM

21co

mpo

nent

arch

itect

ure,

ther

eby

enab

ling

the

use

ofst

anda

lone

XU

L22

appl

icat

ions

inPy

thon

.T

heX

UL

tool

kith

astr

aditi

onal

lybe

enw

rapp

edup

inva

riou

s

19http://www.riverbankcomputing.co.uk/pykde/index.php

20http://developer.mozilla.org/en/docs/PyXPCOM

21http://developer.mozilla.org/en/docs/XPCOM

22http://developer.mozilla.org/en/docs/XUL

othe

rpar

tsof

XPC

OM

,but

with

the

adve

ntof

libxu

land

XU

LRun

ner23

this

shou

ldbe

com

em

ore

feas

ible

.

pt:P

ytho

n/Pr

ogra

maç

ãoco

mG

UI24

23http://developer.mozilla.org/en/docs/XULRunner

24http://pt.wikibooks.org/wiki/Python%2FPrograma%E7%E3o%

20com%20GUI

23G

ame

Prog

ram

min

gin

Pyth

on

23.1

3DG

ame

Prog

ram

min

g

23.1

.13D

Gam

eE

ngin

ew

itha

Pyth

onbi

ndin

g

•Ir

rlic

htE

ngin

ehttp

://ir

rlic

ht.s

ourc

efor

ge.n

et/1

(Pyt

hon

bind

ing

web

site

:ht

tp://

pypi

.pyt

hon.

org/

pypi

/pyi

rrlic

ht2

)

1http://irrlicht.sourceforge.net/

2http://pypi.python.org/pypi/pyirrlicht

263

•O

gre

Eng

ine

http

://w

ww

.ogr

e3d.

org/

3(P

ytho

nbi

ndin

gw

ebsi

te:

http

://w

ww

.pyt

hon-

ogre

.org

/4)

Bot

har

eve

rygo

odfr

eeop

enso

urce

C++

3Dga

me

Eng

ine

with

aPy

thon

bind

ing.

•C

ryst

alSp

ace5

isa

free

cros

s-pl

atfo

rmso

ftwar

ede

velo

pmen

tkit

forr

eal-t

ime

3Dgr

aphi

cs,w

ithpa

rtic

ular

focu

son

gam

es.

Cry

stal

Spac

eis

acce

ssib

lefr

omPy

thon

intw

ow

ays:

(1)

asa

Cry

stal

Spac

epl

ugin

mod

ule

inw

hich

C++

code

can

call

upon

Pyth

onco

de,a

ndin

whi

chPy

thon

code

can

call

upon

Cry

stal

Spac

e;(2

)as

apu

rePy

thon

mod

ule

nam

ed‘c

spac

e’w

hich

one

can

‘im

port

’fro

mw

ithin

Pyth

onpr

ogra

ms.

Tous

eth

efir

stop

tion,

load

the

‘csp

ytho

n’pl

ugin

asyo

uw

ould

load

any

othe

rC

ryst

alSp

ace

plug

in,a

ndin

tera

ctw

ithit

via

the

SCF

‘iSc

ript

’int

erfa

ce.T

hese

cond

appr

oach

allo

ws

3http://www.ogre3d.org/

4http://www.python-ogre.org/

5http://www.crystalspace3d.org

you

tow

rite

Cry

stal

Spac

eap

plic

atio

nsen

tirel

yin

Pyth

on,w

ithou

tany

C++

codi

ng.

CS

Wik

i6

23.1

.23D

Gam

eE

ngin

esw

ritt

enfo

rPy

thon

Eng

ines

desi

gned

forP

ytho

nfr

omsc

ratc

h.

•B

lend

er7

isan

impr

essi

ve3D

tool

with

afu

llyin

tegr

ated

3Dgr

aphi

cscr

eatio

nsu

iteal

low

ing

mod

elin

g,an

imat

ion,

rend

erin

g,po

st-p

rodu

ctio

n,re

al-t

ime

inte

ract

ive

3Dan

dga

me

crea

tion

and

play

back

with

cros

s-pl

atfo

rmco

mpa

ti-bi

lity.

The

3Dga

me

engi

neus

esan

embe

dded

pyth

onin

terp

rete

rto

mak

e3D

gam

es.

•Py

Soy8

isa

3dcl

oud

gam

een

gine

forP

ytho

n3.

Itw

asde

sign

edfo

rrap

idde

velo

pmen

twith

anin

tuiti

veA

PIth

atge

tsne

wga

me

deve

lope

rsst

arte

d

6http://en.wikipedia.org/wiki/Crystal_Space

7http://www.blender.org/

8http://www.pysoy.org/

quic

kly.

The

clou

dga

min

g9de

sign

allo

ws

PySo

yga

mes

tobe

play

edon

ase

rver

with

outd

ownl

oadi

ngth

em,g

reat

lyre

duci

ngth

eco

mpl

exity

ofga

me

dist

ribu

tion.

XM

PP10

acco

unts

(suc

has

Jabb

eror

GM

ail)

can

beus

edfo

ron

line

gam

ing

iden

titie

s,ch

at,a

ndin

itiat

ing

conn

ectio

nsto

gam

ese

rver

s.Py

Soy

isre

leas

edun

dert

heG

NU

AG

PLlic

ense

11.

•So

ya12

isa

3Dga

me

engi

new

ithan

easy

toun

ders

tand

desi

gn.I

tsw

ritte

nin

the

Pyre

x13pr

ogra

mm

ing

lang

uage

and

uses

Cal

3dfo

ran

imat

ion

and

OD

E14

forp

hysi

cs.S

oya

isav

aila

ble

unde

rthe

GN

UG

PLlic

ense

15.

•Pa

nda3

D16

isa

3Dga

me

engi

ne.I

t'sa

libra

ryw

ritte

nin

C++

with

Pyth

onbi

ndin

gs.P

anda

3Dis

desi

gned

inor

dert

osu

ppor

tash

ortl

earn

ing

curv

ean

d

9http://en.wikipedia.org/wiki/Cloud_gaming

10http://en.wikipedia.org/wiki/XMPP

11http://en.wikipedia.org/wiki/GNU_AGPL

12http://www.soya3d.org/

13http://en.wikipedia.org/wiki/Pyrex%20programming%

20language

14http://en.wikipedia.org/wiki/Open%20Dynamics%20Engine

15http://en.wikipedia.org/wiki/GNU_GPL

16http://www.panda3d.org/

rapi

dde

velo

pmen

t.Th

isso

ftwar

eis

avai

labl

efo

rfre

edo

wnl

oad

with

sour

ceco

deun

der

the

BSD

Lic

ense

.T

hede

velo

pmen

twas

star

ted

by[D

isne

y].

Now

ther

ear

em

any

proj

ects

mad

ew

ithPa

nda3

D,s

uch

asD

isne

y's

Pira

te's

ofth

eC

arib

bean

Onl

ine17

,To

onTo

wn18

,B

uild

ing

Vir

tual

Wor

ld19

,Sc

hell

Gam

es20

and

man

yot

hers

.Pan

da3D

supp

orts

seve

ralf

eatu

res:

Proc

edur

alG

eom

etry

,Ani

mat

edTe

xtur

e,R

ende

rto

text

ure,

Trac

km

otio

n,fo

g,pa

rtic

lesy

stem

,and

man

yot

hers

.•

Cry

stal

Spac

e21Is

a3D

gam

een

gine

,w

itha

Pyth

onbi

ndin

gs,

nam

ed*

PyC

ryst

al22

,vie

wW

ikip

edia

page

of*

Cry

stal

Spac

e23.

17http://disney.go.com/pirates/online/

18http://www.toontown.com/

19http://www.etc.cmu.edu/bvw

20http://www.schellgames.com

21http://www.crystalspace3d.org/

22http://www.crystalspace3d.org/main/PyCrystal

23http://en.wikipedia.org/wiki/Crystalspace

23.2

2DG

ame

Prog

ram

min

g

•Py

gam

e24is

acr

oss

plat

form

Pyth

onlib

rary

whi

chw

raps

SDL25

.Itp

rovi

des

man

yfe

atur

eslik

eSp

rite

grou

psan

dso

und/

imag

elo

adin

gan

dea

sych

angi

ngof

anob

ject

spo

sitio

n.It

also

prov

ides

the

prog

ram

mer

acce

ssto

key

and

mou

seev

ents

.•

Phil'

sPy

gam

eU

tiliti

es(P

GU

)26is

aco

llect

ion

ofto

ols

and

libra

ries

that

enha

nce

Pyga

me.

Tool

sin

clud

ea

tile

edito

ran

da

leve

ledi

tor27

(tile

,iso

-m

etri

c,he

xago

nal)

.GU

Ienh

ance

men

tsin

clud

efu

llfe

atur

edG

UI,

HT

ML

rend

erin

g,do

cum

ent

layo

ut,

and

text

rend

erin

g.T

helib

rari

esin

clud

ea

spri

tean

dtil

een

gine

28(t

ile,i

som

etri

c,he

xago

nal)

,ast

ate

engi

ne,a

timer

,an

da

high

scor

esy

stem

.(B

eta

with

last

upda

teM

arch

,20

07.

API

sto

bede

prec

ated

and

isom

etri

can

dhe

xago

nals

uppo

rtis

curr

ently

Alp

haan

d

24http://en.wikipedia.org/wiki/Pygame

25http://en.wikipedia.org/wiki/SDL

26http://www.imitationpickles.org/pgu/wiki/index

27http://en.wikipedia.org/wiki/Level_editor

28http://en.wikipedia.org/wiki/Tile_engine

subj

ectt

och

ange

.)[U

pdat

e27

/02/

08A

utho

rin

dica

tes

heis

notc

urre

ntly

activ

ely

deve

lopi

ngth

islib

rary

and

anyo

neth

atis

will

ing

tode

velo

pth

eir

own

scro

lling

isom

etri

clib

rary

offe

ring

can

use

the

exis

ting

code

inPG

Uto

gett

hem

star

ted.

]•

Pygl

et29

isa

cros

s-pl

atfo

rmw

indo

win

gan

dm

ultim

edia

libra

ryfo

rPyt

hon

with

noex

tern

alde

pend

enci

esor

inst

alla

tion

requ

irem

ents

.Pyg

letp

rovi

des

anob

ject

-ori

ente

dpr

ogra

mm

ing

inte

rfac

efo

rdev

elop

ing

gam

esan

dot

her

visu

ally

-ric

hap

plic

atio

nsfo

rWin

dow

s30,M

acO

SX

31an

dL

inux

32.P

ygle

tal

low

spr

ogra

ms

toop

enm

ultip

lew

indo

ws

onm

ultip

lesc

reen

s,dr

awin

thos

ew

indo

wsw

ithO

penG

L,an

dpl

ayba

ckau

dio

and

vide

oin

mos

tfor

mat

s.U

nlik

esi

mila

rlib

rarie

sav

aila

ble,

pygl

etha

sno

exte

rnal

depe

nden

cies

(suc

has

SDL

)and

isw

ritte

nen

tirel

yin

Pyth

on.P

ygle

tis

avai

labl

eun

dera

BSD

-St

yle

licen

se33

.

29http://www.pyglet.org/

30http://en.wikipedia.org/wiki/Windows

31http://en.wikipedia.org/wiki/Mac_OS_X

32http://en.wikipedia.org/wiki/Linux

33http://en.wikipedia.org/wiki/BSD_licenses

•K

ivy34

Kiv

yis

alib

rary

ford

evel

opin

gm

ulti-

touc

hap

plic

atio

ns.I

tis

com

-pl

etel

ycr

oss-

plat

form

(Lin

ux/O

SX/W

in&

And

roid

with

Ope

nGL

ES2

).It

com

esw

ithna

tive

supp

ortf

orm

any

mul

ti-to

uch

inpu

tdev

ices

,agr

owin

glib

rary

ofm

ulti-

touc

haw

are

wid

gets

and

hard

war

eac

cele

rate

dO

penG

Ldr

awin

g.K

ivy

isde

sign

edto

lety

oufo

cus

onbu

ildin

gcu

stom

and

high

lyin

tera

ctiv

eap

plic

atio

nsas

quic

kly

and

easi

lyas

poss

ible

.•

Rab

byt35

Afa

stSp

rite

36lib

rary

for

Pyth

onw

ithga

me

deve

lopm

ent

inm

ind.

With

Rab

bytA

nim

s,ev

enol

dgr

aphi

csca

rds

can

prod

uce

very

fast

anim

atio

nsof

2,40

0or

mor

esp

rite

sha

ndlin

gpo

sitio

n,ro

tatio

n,sc

alin

g,an

dco

lors

imul

tane

ousl

y.

34http://kivy.org/

35http://arcticpaint.com/projects/rabbyt/

36http://en.wikipedia.org/wiki/Sprite_%28computer_graphics%

29

23.3

See

Als

o

•10

Les

sons

Lea

rned

37-

How

ToB

uild

aG

ame

InA

Wee

kFr

omSc

ratc

hW

ithN

oB

udge

t

37http://www.gamedev.net/reference/articles/article2259.asp

24So

cket

s

24.1

HT

TP

Clie

nt

Mak

ea

very

sim

ple

HT

TP

clie

nt

import

socket

s=

socket.socket()

s.connect(('localhost',

80))

s.send('GET

/HTTP/1.1\nHost:localhost\n\n')

s.recv(40000)

#receive

40000

bytes

273

24.2

NT

P/So

cket

s

Con

nect

ing

toan

dre

adin

gan

NT

Ptim

ese

rver

,ret

urni

ngth

etim

eas

follo

ws

ntpps

picoseconds

portion

of

time

ntps

seconds

portion

of

time

ntpms

milliseconds

portion

of

time

ntpt

64-bit

ntp

time,

seconds

in

upper

32-bits,

picoseconds

in

lower

32-bits

25Fi

les

25.1

File

I/O

Rea

den

tire

file:

inputFileText

=open("testit.txt",

"r").read()

print(inputFileText)

Inth

isca

seth

e"r

"pa

ram

eter

mea

nsth

efil

ew

illbe

open

edin

read

-onl

ym

ode.

Rea

dce

rtai

nam

ount

ofby

tes

from

afil

e:

275

inputFileText

=open("testit.txt",

"r").read(123)

print(inputFileText)

Whe

nop

enin

ga

file,

one

star

tsre

adin

gat

the

begi

nnin

gof

the

file,

ifon

ew

ould

wan

tmor

era

ndom

acce

ssto

the

file,

itis

poss

ible

tous

eseek()

toch

ange

the

curr

entp

ositi

onin

afil

ean

dtell()

toge

tto

know

the

curr

ent

posi

tion

inth

efil

e.T

his

isill

ustr

ated

inth

efo

llow

ing

exam

ple:

>>>

f=open("/proc/cpuinfo","r")

>>>

f.tell()

0L>>>

f.read(10)

'processor\t'

>>>

f.read(10)

':

0\nvendor'

>>>

f.tell()

20L

>>>

f.seek(10)

>>>

f.tell()

10L

>>>

f.read(10)

':

0\nvendor'

>>>

f.close()

>>>

f<closed

file

'/proc/cpuinfo',

mode

'r'

at

0xb7d79770>

Her

ea

file

isop

ened

,tw

ice

ten

byte

sar

ere

ad,tell()

show

sth

atth

ecu

rren

tof

fset

isat

posi

tion

20,n

owseek()

isus

edto

goba

ckto

posi

tion

10(t

hesa

me

posi

tion

whe

reth

ese

cond

read

was

star

ted)

and

ten

byte

sar

ere

adan

dpr

inte

dag

ain.

And

whe

nno

mor

eop

erat

ions

ona

file

are

need

edth

eclose()

func

tion

isus

edto

clos

eth

efil

ew

eop

ened

.

Rea

don

elin

eat

atim

e:

for

line

in

open("testit.txt",

"r"):

printline

Inth

isca

sereadlines()

will

retu

rnan

arra

yco

ntai

ning

the

indi

vidu

allin

esof

the

file

asar

ray

entr

ies.

Rea

ding

asi

ngle

line

can

bedo

neus

ing

thereadline()

func

tion

whi

chre

turn

sth

ecu

rren

tlin

eas

ast

ring

.T

his

exam

ple

will

outp

utan

addi

tiona

lne

wlin

ebe

twee

nth

ein

divi

dual

lines

of

the

file,

this

isbe

caus

eon

eis

read

from

the

file

and

prin

tint

rodu

ces

anot

her

new

line.

Wri

teto

afil

ere

quir

esth

ese

cond

para

met

erofopen()

tobe

"w",

this

will

over

wri

teth

eex

istin

gco

nten

tsof

the

file

ifit

alre

ady

exis

tsw

hen

open

ing

the

file:

outputFileText

="Here's

some

text

to

save

in

afile"

open("testit.txt",

"w").write(outputFileText)

App

end

toa

file

requ

ires

the

seco

ndpa

ram

eter

ofopen()

tobe

"a"

(fro

map

pend

):

outputFileText

="Here's

some

text

to

add

to

the

existing

file."

open("testit.txt",

"a").write(outputFileText)

Not

eth

atth

isdo

esno

tadd

alin

ebr

eak

betw

een

the

exis

ting

file

cont

enta

ndth

est

ring

tobe

adde

d.

As

anot

her

impo

rtan

tex

ampl

e,if

you

wan

tto

read

alis

tof

num

bers

ina

file(

both

indi

ffer

entl

ines

,and

sam

elin

es),

and

putt

henu

mbe

rsin

one

line

near

each

othe

r,se

para

teth

enu

mbe

rsin

diff

eren

tlin

es,i

na

list,

one

fast

way

wou

ldbe

:

f=

open("C:\Documents

and

Settings\Pardis

Rayan\Desktop\SCC\SCC.txt","r")

g=

[[int(i)for

iin

line.split()

]forline

in

f]

25.2

Test

ing

File

s

Det

erm

ine

whe

ther

path

exis

ts:

import

os

os.path.exists('<path

string>')

Whe

nw

orki

ngon

syst

ems

such

asM

icro

soft

Win

dow

s™,t

hedi

rect

ory

sepa

-ra

tors

will

confl

ictw

ithth

epa

thst

ring

.To

geta

roun

dth

is,d

oth

efo

llow

ing:

import

os

os.path.exists('C:\\windows\\example\\path')

Abe

tterw

ayho

wev

eris

tous

e"r

aw",

orr

:

import

os

os.path.exists(r'C:\windows\example\path')

But

ther

ear

eso

me

othe

rco

nven

ient

func

tions

inos.path

,w

here

path.code.exists()

only

confi

rms

whe

ther

orno

tpa

thex

ists

,th

ere

are

func

tions

whi

chle

tyou

know

ifth

epa

this

afil

e,a

dire

ctor

y,a

mou

ntpo

into

rasy

mlin

k.Th

ere

isev

ena

func

tionos.path.realpath()

whi

chre

veal

sth

etr

uede

stin

atio

nof

asy

mlin

k:

>>>

import

os

>>>

os.path.isfile("/")

False

>>>

os.path.isfile("/proc/cpuinfo")

True

>>>

os.path.isdir("/")

True

>>>

os.path.isdir("/proc/cpuinfo")

False

>>>

os.path.ismount("/")

True

>>>

os.path.islink("/")

False

>>>

os.path.islink("/vmlinuz")

True

>>>

os.path.realpath("/vmlinuz")

'/boot/vmlinuz-2.6.24-21-generic'

25.3

Com

mon

File

Ope

ratio

ns

Toco

pyor

mov

ea

file,

use

the

shut

illib

rary

.

import

shutil

shutil.move("originallocation.txt","newlocation.txt")

shutil.copy("original.txt","copy.txt")

Tope

rfor

ma

recu

rsiv

eco

pyit

ispo

ssib

leto

usecopytree()

,to

perf

orm

are

curs

ive

rem

ove

itis

poss

ible

tous

ermtree()

import

shutil

shutil.copytree("dir1","dir2")

shutil.rmtree("dir1")

Tore

mov

ean

indi

vidu

alfil

eth

ere

exis

tsth

eremove()

func

tion

inth

eos

mod

ule:

import

os

os.remove("file.txt")

26D

atab

ase

Prog

ram

min

g

26.1

Gen

eric

Dat

abas

eC

onne

ctiv

ityus

ing

OD

BC

The

Ope

nD

atab

ase

Con

nect

ivity

1(O

DB

C)A

PIst

anda

rdal

low

str

ansp

aren

tco

nnec

tions

with

any

data

base

that

supp

orts

the

inte

rfac

e.T

his

incl

udes

mos

tpo

pula

rdat

abas

es,s

uch

asPo

stgr

eSQ

L2

orM

icro

soft

Acc

ess3 .T

hest

reng

ths

1http://en.wikipedia.org/wiki/Open%20Database%

20Connectivity

2http://en.wikipedia.org/wiki/PostgreSQL

3http://en.wikipedia.org/wiki/Microsoft%20Access

283

ofus

ing

this

inte

rfac

eis

that

aPy

thon

scrip

torm

odul

eca

nbe

used

ondi

ffer

ent

data

base

sby

only

mod

ifyi

ngth

eco

nnec

tion

stri

ng.

The

rear

eth

ree

OD

BC

mod

ules

forP

ytho

n:

1.Py

thon

Win

OD

BC

Mod

ule:

prov

ided

byM

ark

Ham

mon

dw

ithth

ePy

thon

Win

4pa

ckag

efo

rMic

roso

ftW

indo

ws

(onl

y).T

his

isa

min

imal

impl

emen

tatio

nof

OD

BC

,and

conf

orm

sto

Ver

sion

1.0

ofth

ePy

thon

Dat

abas

eA

PI.A

lthou

ghit

isst

able

,itw

illlik

ely

notb

ede

velo

ped

any

furt

her.5

2.m

xOD

BC

:a

com

mer

cial

Pyth

onpa

ckag

e(h

ttp://

ww

w.e

geni

x.co

m/p

rodu

cts/

pyth

on/m

xOD

BC

/),6

whi

chfe

atur

esha

ndlin

gof

Dat

eTim

eob

ject

san

dpr

epar

edst

atem

ents

(usi

ngpa

ram

eter

s).

4http://starship.python.net/crew/mhammond/win32/

5H

amm

ond,

M.P

ytho

nPr

ogra

mm

ing

onW

in32

.O'R

eilly

,,20

006

http://www.egenix.com/products/python/mxODBC/),

3.py

odbc

:an

open

-sou

rce

Pyth

onpa

ckag

e(h

ttp://

code

.goo

gle.

com

/p/p

yodb

c),7

whi

chus

eson

lyna

tive

Pyth

onda

ta-ty

pes

and

uses

prep

ared

stat

emen

tsfo

rinc

reas

edpe

rfor

man

ce.T

hepr

esen

tver

sion

supp

orts

the

Pyth

onD

atab

ase

API

Spec

ifica

tion

v2.0

.8

26.1

.1py

odbc

An

exam

ple

usin

gth

epyodbc

Pyth

onpa

ckag

ew

itha

Mic

roso

ftA

cces

sfil

e(a

lthou

ghth

isda

taba

seco

nnec

tion

coul

dju

stas

easi

lybe

aM

ySQ

Lda

taba

se):

import

pyodbc

DBfile

='/data/MSAccess/Music_Library.mdb'

conn

=pyodbc.connect('DRIVER={Microsoft

Access

Driver

(*.mdb)};DBQ='+DBfile)

cursor

=conn.cursor()

7http://code.google.com/p/pyodbc),

8Py

thon

Dat

abas

eA

PISp

ecifi

catio

nv2

.09 .P

ytho

n.R

etri

eved

SQL

='SELECT

Artist,

AlbumName

FROM

RecordCollection

ORDER

BY

Year;'

for

row

in

cursor.execute(SQL):

#cursors

are

iterable

printrow.Artist,

row.AlbumName

cursor.close()

conn.close()

Man

ym

ore

feat

ures

and

exam

ples

are

prov

ided

onth

epy

odbc

web

site

.

26.2

Post

gres

conn

ectio

nin

Pyth

on

->se

ePy

thon

Prog

ram

min

g/D

atab

ases

10

10http://en.wikibooks.org/wiki/Python%20Programming%

2FDatabases

26.3

MyS

QL

conn

ectio

nin

Pyth

on

->se

ePy

thon

Prog

ram

min

g/D

atab

ases

11

26.4

SQL

Alc

hem

yin

Act

ion

SQL

Alc

hem

yha

sbe

com

eth

efa

vori

tech

oice

form

any

larg

ePy

thon

proj

ects

that

use

data

base

s.A

long

,up

date

dlis

tof

such

proj

ects

islis

ted

onth

eSQ

LA

lche

my

site

.Add

ition

ally

,apr

etty

good

tuto

rial

can

befo

und

ther

e,as

wel

l.A

long

with

ath

inda

taba

sew

rapp

er,E

lixir,

itbe

have

sve

rysi

mila

rly

toth

eO

RM

inR

ails

,Act

iveR

ecor

d.

11http://en.wikibooks.org/wiki/Python%20Programming%

2FDatabases

26.5

See

also

•Py

thon

Prog

ram

min

g/D

atab

ases

12

26.6

Ref

eren

ces

26.7

Ext

erna

llin

ks

•SQ

LA

lche

my13

•SQ

LO

bjec

t14

•PE

P24

915-P

ytho

nD

atab

ase

API

Spec

ifica

tion

v2.0

12http://en.wikibooks.org/wiki/Python%20Programming%

2FDatabases

13http://www.sqlalchemy.org/

14http://www.sqlobject.org/

15http://www.python.org/dev/peps/pep-0249/

•D

atab

ase

Topi

cG

uide

16on

pyth

on.o

rg

16http://www.python.org/doc/topics/database/

27W

ebPa

geH

arve

stin

g

291

28T

hrea

ding

Thr

eadi

ngin

pyth

onis

used

toru

nm

ultip

leth

read

s(t

asks

,fun

ctio

nca

lls)a

tth

esa

me

time.

Not

eth

atth

isdo

esno

tmea

n,th

atth

eyar

eex

ecut

edon

diff

eren

tC

PUs.

Pyth

onth

read

sw

illN

OT

mak

eyo

urpr

ogra

mfa

ster

ifit

alre

ady

uses

100

%C

PUtim

e,pr

obab

lyyo

uth

enw

antt

olo

okin

topa

ralle

lpro

gram

min

g.If

you

are

inte

rest

edin

para

llelp

roga

mm

ing

with

pyth

on,p

leas

ese

ehe

re1 .

Pyth

onth

read

sar

eus

edin

case

sw

here

the

exec

utio

nof

ata

skin

volv

esso

me

wai

ting.

One

exam

ple

wou

ldbe

inte

ract

ion

with

ase

rvic

eho

sted

onan

othe

r

1http://wiki.python.org/moin/ParallelProcessing

293

com

pute

r,su

chas

aw

ebse

rver

.Thr

eadi

ngal

low

spy

thon

toex

ecut

eot

herc

ode

whi

lew

aitin

g;th

isis

easi

lysi

mul

ated

with

the

slee

pfu

nctio

n.

28.1

Exa

mpl

es

28.1

.1A

Min

imal

Exa

mpl

ew

ithFu

nctio

nC

all

Mak

ea

thre

adth

atpr

ints

num

bers

from

1-10

,wai

tsfo

r1se

cbe

twee

n:

import

thread

import

time

def

loop1_10():

fori

in

range(1,

11):

time.sleep(1)

print(i)

thread.start_new_thread(loop1_10,

())

28.1

.2A

Min

imal

Exa

mpl

ew

ithO

bjec

t

#!/usr/bin/env

python

import

threading

import

time

from

__future__

import

print_function

class

MyThread(threading.Thread):

defrun(self):

print("{}

started!".format(self.getName()))

#"Thread-x

started!"

time.sleep(1)

#Pretend

to

workfora

second

print("{}

finished!".format(self.getName()))

#"Thread-x

finishsed!"

if

__name__==

'__main__':

forx

in

range(4):

#Four

times... mythread

=MyThread(name

="Thread-{}".format(x

+1))

#...Instantiate

athread

andpass

aunique

ID

to

it

mythread.start()

#...Start

the

thread

time.sleep(.9)

#...Wait

0.9

seconds

before

starting

another

Thi

ssh

ould

outp

ut:

Thread-1

started!

Thread-2

started!

Thread-1

finished!

Thread-3

started!

Thread-2

finished!

Thread-4

started!

Thread-3

finished!

Thread-4

finished!

Not

e:th

isex

ampl

eap

pear

sto

cras

hID

LE

inW

indo

ws

XP

(see

ms

tow

ork

inID

LE

1.2.

4in

Win

dow

sX

Pth

ough

)

The

rese

ems

tobe

apr

oble

mw

ithth

is,i

fyou

repl

ace

Slee

p(1)

with

(2),

and

chan

gera

nge

(4)

tora

nge(

10).

Thr

ead

-2fin

ishe

dis

the

first

line

befo

reits

even

star

ted.

inW

ING

IDE

,Net

bean

s,ec

lipse

isfin

e.

29E

xten

ding

with

C

Thi

sgi

ves

am

inim

alE

xam

ple

onho

wto

Ext

end

Pyth

onw

ithC

.Lin

uxis

used

forb

uild

ing

(fee

lfre

eto

exte

ndit

foro

ther

Plat

form

s).I

fyou

have

any

prob

lem

s,pl

ease

repo

rtth

em(e

.g.o

nth

edi

cuss

ion

page

),Iw

illch

eck

back

ina

whi

lean

dtr

yto

sort

them

out.

29.1

Usi

ngth

ePy

thon

/CA

PI

On

anU

bunt

usy

stem

,you

mig

htne

edto

run

297

$sudo

apt-get

install

python-dev

•ht

tp://

docs

.pyt

hon.

org/

ext/e

xt.h

tml

•ht

tp://

docs

.pyt

hon.

org/

api/a

pi.h

tml

29.1

.1A

min

imal

exam

ple

The

min

imal

exam

ple

we

will

crea

teno

wis

very

sim

ilari

nbe

havi

ourt

oth

efo

llow

ing

pyth

onsn

ippe

t:

def

say_hello(name):

"Greet

somebody."

print"Hello

%s!"

%name

The

Cso

urce

code

(hellomodule.c

)

#include

<Python.h>

static

PyObject*

say_hello(PyObject*self,

PyObject*args)

{constchar*

name;

if(!PyArg_ParseTuple(args,

"s",

&name))

returnNULL;

printf("Hello

%s!\n",

name);

Py_RETURN_NONE;

} static

PyMethodDef

HelloMethods[]

={

{"say_hello",

say_hello,

METH_VARARGS,

"Greet

somebody."},

{NULL,

NULL,

0,

NULL}

};

PyMODINIT_FUNC

inithello(void)

{(void)

Py_InitModule("hello",

HelloMethods);

} Bui

ldin

gth

eex

tens

ion

mod

ule

with

GC

Cfo

rL

inux

Tobu

ildou

rext

ensi

onm

odul

ew

ecr

eate

the

filesetup.py

like:

from

distutils.core

import

setup,

Extension

module1

=Extension('hello',

sources

=['hellomodule.c'])

setup

(name

='PackageName',

version

='1.0',

description

='This

is

ademo

package',

ext_modules

=[module1])

Now

we

can

build

ourm

odul

ew

ith

python

setup.py

build

The

mod

ulehello.so

will

end

upinbuild/lib.linux-i686-x.y

.

Bui

ldin

gth

eex

tens

ion

mod

ule

with

GC

Cfo

rM

icro

soft

Win

dow

s

Mic

roso

ftW

indo

ws

user

sca

nus

eM

inG

W1

toco

mpi

leth

isfr

omcmd.exe2

usin

ga

sim

ilar

met

hod

toL

inux

user

,as

show

nab

ove.

Ass

umin

ggcc

isin

thePATH

envi

ronm

entv

aria

ble,

type

:

python

setup.py

build

-cmingw32

1http://en.wikipedia.org/wiki/MinGW

2http://en.wikipedia.org/wiki/cmd.exe

The

mod

ulehello.pyd

will

end

upinbuild\lib.win32-x.y

,whi

chis

aPy

thon

Dyn

amic

Mod

ule

(sim

ilart

oaDLL

).

An

alte

rnat

ew

ayof

build

ing

the

mod

ule

inW

indo

ws

isto

build

aD

LL

.(T

his

met

hod

does

notn

eed

anex

tens

ion

mod

ule

file)

.Fro

mcmd.exe

,typ

e:

gcc

-c

hellomodule.c

-I/PythonXY/include

gcc

-shared

hellomodule.o

-L/PythonXY/libs

-lpythonXY-o

hello.dll

whe

reX

Yre

pres

ents

the

vers

ion

ofPy

thon

,suc

has

"24"

forv

ersi

on2.

4.

Bui

ldin

gth

eex

tens

ion

mod

ule

usin

gM

icro

soft

Vis

ualC

++

With

VC

8di

stut

ilsis

brok

en.

We

will

use

cl.e

xefr

oma

com

man

dpr

ompt

inst

ead:

cl

/LD

hellomodule.c

/Ic:\Python24\include

c:\Python24\libs\python24.lib

/link/out:hello.dll

Usi

ngth

eex

tens

ion

mod

ule

Cha

nge

toth

esu

bdir

ecto

ryw

here

the

file

‘hel

lo.s

o‘re

side

s.In

anin

tera

ctiv

epy

thon

sess

ion

you

can

use

the

mod

ule

asfo

llow

s.

>>>

import

hello

>>>

hello.say_hello("World")

Hello

World!

29.1

.2A

mod

ule

for

calc

ulat

ing

fibon

acci

num

bers

The

Cso

urce

code

(fibm

odul

e.c)

#include

<Python.h>

int

_fib(intn)

{if(n

<2)

returnn;

elsereturn_fib(n-1)

+_fib(n-2);

} static

PyObject*fib(PyObject*self,

PyObject*args)

{intn;

if(!PyArg_ParseTuple(args,

"i",

&n))

returnNULL;

returnPy_BuildValue("i",

_fib(n));

}

static

PyMethodDef

FibMethods[]

={

{"fib",

fib,

METH_VARARGS,

"Calculate

the

Fibonacci

numbers."},

{NULL,

NULL,

0,

NULL}

};

PyMODINIT_FUNC

initfib(void)

{(void)

Py_InitModule("fib",

FibMethods);

} The

build

scri

pt(s

etup

.py)

from

distutils.core

import

setup,

Extension

module1

=Extension('fib',

sources

=['fibmodule.c'])

setup

(name

='PackageName',

version

='1.0',

description

='This

is

ademo

package',

ext_modules

=[module1])

How

tous

eit?

>>>

import

fib

>>>

fib.fib(10)

55

29.2

Usi

ngSW

IG

Cre

atin

gth

epr

evio

usex

ampl

eus

ing

SWIG

ism

uch

mor

est

raig

htfo

rwar

d.To

follo

wth

ispa

thyo

une

edto

get

SWIG

3up

and

runn

ing

first

.To

inst

alli

ton

anU

bunt

usy

stem

,you

mig

htne

edto

run

the

follo

win

gco

mm

ands

$sudo

apt-get

install

libboost-python-dev

$sudo

apt-get

install

python-dev

Aft

erth

atcr

eate

two

files

.

3http://www.swig.org/

/*hellomodule.c*/

#include

<stdio.h>

void

say_hello(constchar*name)

{printf("Hello

%s!\n",

name);

} /*hello.i*/

%module

hello

extern

voidsay_hello(constchar*name);

Now

com

esth

em

ore

diffi

cult

part

,glu

ing

ital

ltog

ethe

r.

Firs

twe

need

tole

tSW

IGdo

itsw

ork.

swig

-python

hello.i

Thi

sgi

ves

usth

efil

es‘h

ello

.py‘

and

‘hel

lo_w

rap.

c‘.

The

next

step

isco

mpi

ling

(sub

stitu

te/u

sr/in

clud

e/py

thon

2.4/

with

the

corr

ect

path

fory

ours

etup

!).

gcc

-fpic

-c

hellomodule.c

hello_wrap.c

-I/usr/include/python2.4/

Now

linki

ngan

dw

ear

edo

ne!

gcc

-shared

hellomodule.o

hello_wrap.o

-o

_hello.so

The

mod

ule

isus

edin

the

follo

win

gw

ay.

>>>

import

hello

>>>

hello.say_hello("World")

Hello

World!

30E

xten

ding

with

C++

Boo

st.P

ytho

n1is

the

defa

cto

stan

dard

for

wri

ting

C++

2ex

tens

ion

mod

ules

.B

oost

.Pyt

hon

com

esbu

ndle

dw

ithth

eB

oost

C++

Lib

rari

es3 .T

oin

stal

lito

nan

Ubu

ntu

syst

em,y

oum

ight

need

toru

nth

efo

llow

ing

com

man

ds

$sudo

apt-get

install

libboost-python-dev

$sudo

apt-get

install

python-dev

1http://www.boost.org/libs/python/doc/

2http://en.wikibooks.org/wiki/C%2B%2B

3http://www.boost.org/

309

30.1

AH

ello

Wor

ldE

xam

ple

30.1

.1T

heC

++so

urce

code

(hel

lom

odul

e.cp

p)

#include

<iostream>

using

namespace

std;

void

say_hello(constchar*name)

{cout

<<

"Hello

"<<

name

<<

"!\n";

} #include

<boost/python/module.hpp>

#include

<boost/python/def.hpp>

using

namespace

boost::python;

BOOST_PYTHON_MODULE(hello)

{def("say_hello",

say_hello);

}

30.1

.2se

tup.

py

#!/usr/bin/env

python

from

distutils.core

import

setup

from

distutils.extension

import

Extension

setup(name="PackageName",

ext_modules=[

Extension("hello",

["hellomodule.cpp"],

libraries

=["boost_python"])

])

Now

we

can

build

ourm

odul

ew

ith

python

setup.py

build

The

mod

ule

‘hel

lo.s

o‘w

illen

dup

ine.

g‘b

uild

/lib.

linux

-i68

6-2.

4‘.

30.1

.3U

sing

the

exte

nsio

nm

odul

e

Cha

nge

toth

esu

bdir

ecto

ryw

here

the

file

‘hel

lo.s

o‘re

side

s.In

anin

tera

ctiv

epy

thon

sess

ion

you

can

use

the

mod

ule

asfo

llow

s.

>>>

import

hello

>>>

hello.say_hello("World")

Hello

World!

30.2

An

exam

ple

with

CG

AL

Som

e,bu

tnot

all,

func

tions

ofth

eC

GA

Llib

rary

have

alre

ady

Pyth

onbi

ndin

gs.

Her

ean

exam

ple

ispr

ovid

edfo

raca

sew

ithou

tsuc

ha

bind

ing

and

how

itm

ight

beim

plem

ente

d.T

heex

ampl

eis

take

nfr

omth

eC

GA

LD

ocum

enta

tion4 .

4http://www.cgal.org/Manual/3.3/doc_html/cgal_manual/

SearchStructures/Chapter_main.html#Subsection_46.5.1

//

test.cpp

using

namespace

std;

/*

PYTHON*/

#include

<boost/python.hpp>

#include

<boost/python/module.hpp>

#include

<boost/python/def.hpp>

namespace

python

=boost::python;

/*

CGAL*/

#include

<CGAL/Cartesian.h>

#include

<CGAL/Range_segment_tree_traits.h>

#include

<CGAL/Range_tree_k.h>

typedef

CGAL::Cartesian<double>

K;

typedef

CGAL::Range_tree_map_traits_2<K,

char>

Traits;

typedef

CGAL::Range_tree_2<Traits>

Range_tree_2_type;

typedef

Traits::Key

Key;

typedef

Traits::Interval

Interval;

Range_tree_2_type

*Range_tree_2

=newRange_tree_2_type;

void

create_tree()

{

typedefTraits::Key

Key;

typedefTraits::Interval

Interval;

std::vector<Key>

InputList,

OutputList;

InputList.push_back(Key(K::Point_2(8,5.1),

'a'));

InputList.push_back(Key(K::Point_2(1.0,1.1),

'b'));

InputList.push_back(Key(K::Point_2(3,2.1),

'c'));

Range_tree_2->make_tree(InputList.begin(),InputList.end());

Interval

win(Interval(K::Point_2(1,2.1),K::Point_2(8.1,8.2)));

std::cout

<<

"\n

Window

Query:\n";

Range_tree_2->window_query(win,

std::back_inserter(OutputList));

std::vector<Key>::iterator

current=OutputList.begin();

while(current!=OutputList.end()){

std::cout

<<

""

<<

(*current).first.x()

<<

","

<<

(*current).first.y()

<<

":"

<<

(*current).second

<<

std::endl;

current++;

}std::cout

<<

"\n

Done\n";

} void

initcreate_tree()

{;}

using

namespace

boost::python;

BOOST_PYTHON_MODULE(test)

{def("create_tree",

create_tree,

"");

} //

setup.py

#!/usr/bin/env

python

from

distutils.core

import

setup

from

distutils.extension

import

Extension

setup(name="PackageName",

ext_modules=[

Extension("test",

["test.cpp"],

libraries

=["boost_python"])

])

We

then

com

pile

and

run

the

mod

ule

asfo

llow

s:

$python

setup.py

build

$cd

build/lib*

$python

>>>

import

test

>>>

test.create_tree()

Window

Query:

3,2.1:c

8,5.1:a

Done

>>>

30.3

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rors

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can

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#include

<vector>

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std;

void

_afunction_wrapper(intN,

boost::python::list

mapping)

{

intmapping_length

=boost::python::extract<int>(mapping.attr("__len__")());

//Do

Error

checking,

the

mapping

needs

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at

least

as

long

as

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<N)

{PyErr_SetString(PyExc_ValueError,

"The

string

mapping

must

be

at

least

of

length

N");

boost::python::throw_error_already_set();

return;

} vector<string>

mystrings(mapping_length);

for(inti=0;

i<mapping_length;

i++)

{mystrings[i]

=boost::python::extract<charconst

*>(mapping[i]);

}

//now

call

our

C++

function

_afunction(N,

mystrings);

} using

namespace

boost::python;

BOOST_PYTHON_MODULE(c_afunction)

{def("afunction",

_afunction_wrapper);

}

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5http://www.diveintopython.org/

6http://www.ibiblio.org/obp/thinkCSpy/

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17http://en.wikibooks.org/w/index.php?title=User:Benrolfe

18http://en.wikibooks.org/w/index.php?title=User:Betalpha

19http://en.wikibooks.org/w/index.php?title=User:Bittner

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43http://en.wikibooks.org/w/index.php?title=User:Driscoll

44http://en.wikibooks.org/w/index.php?title=User:Edleafe

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48http://en.wikibooks.org/w/index.php?title=User:FerranJorba

49http://en.wikibooks.org/w/index.php?title=User:Fishpi

50http://en.wikibooks.org/w/index.php?title=User:Flarelocke

51http://en.wikibooks.org/w/index.php?title=User:Foxj

52http://en.wikibooks.org/w/index.php?title=User:Fry-kun

53http://en.wikibooks.org/w/index.php?title=User:Gasto5

54http://en.wikibooks.org/w/index.php?title=User:Greyweather

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76http://en.wikibooks.org/w/index.php?title=User:Lena2289

77http://en.wikibooks.org/w/index.php?title=User:Leopold_

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78http://en.wikibooks.org/w/index.php?title=User:Logictheo

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92http://en.wikibooks.org/w/index.php?title=User:Nikai

93http://en.wikibooks.org/w/index.php?title=User:Nikhil389

94http://en.wikibooks.org/w/index.php?title=User:NithinBekal

95http://en.wikibooks.org/w/index.php?title=User:Offpath

96http://en.wikibooks.org/w/index.php?title=User:Panic2k4

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101http://en.wikibooks.org/w/index.php?title=User:Pingveno

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110http://en.wikibooks.org/w/index.php?title=User:Robm351

111http://en.wikibooks.org/w/index.php?title=User:RyanPenner

112http://en.wikibooks.org/w/index.php?title=User:Sigma_7

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119http://en.wikibooks.org/w/index.php?title=User:Tecky2

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125http://en.wikibooks.org/w/index.php?title=User:Tom_Morris

126http://en.wikibooks.org/w/index.php?title=User:Treilly

127http://en.wikibooks.org/w/index.php?title=User:Unionhawk

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,an

dar

eir

revo

cabl

epr

ovid

edth

est

ated

cond

ition

sar

em

et.

Thi

sL

icen

seex

plic

itly

affir

ms

your

unlim

ited

perm

issi

onto

run

the

unm

odifi

edPr

ogra

m.

The

out-

put

from

runn

ing

aco

vere

dw

ork

isco

vere

dby

this

Lic

ense

only

ifth

eou

tput

,gi

ven

itsco

nten

t,co

nstit

utes

aco

vere

dw

ork.

Thi

sL

icen

seac

know

l-ed

ges

your

righ

tsof

fair

use

orot

here

quiv

alen

t,as

prov

ided

byco

pyri

ghtl

aw.

You

may

mak

e,ru

nan

dpr

opa-

gate

cove

red

wor

ksth

atyo

udo

not

conv

ey,

with

out

cond

ition

s

solo

ngas

your

licen

seot

her-

wis

ere

mai

nsin

forc

e.Y

oum

ayco

nvey

cove

red

wor

ksto

othe

rsfo

rth

eso

lepu

rpos

eof

havi

ngth

emm

ake

mod

ifica

tions

excl

u-si

vely

for

you,

orpr

ovid

eyo

uw

ithfa

cilit

ies

for

runn

ing

thos

ew

orks

,pr

ovid

edth

atyo

uco

m-

ply

with

the

term

sof

this

Li-

cens

ein

conv

eyin

gal

lm

ater

ial

for

whi

chyo

udo

not

cont

rol

copy

righ

t.T

hose

thus

mak

ing

orru

nnin

gth

eco

vere

dw

orks

for

you

mus

tdo

soex

clus

ivel

yon

your

beha

lf,

unde

ryo

urdi

-re

ctio

nan

dco

ntro

l,on

term

sth

atpr

ohib

itth

emfr

omm

akin

gan

yco

pies

ofyo

urco

pyri

ghte

dm

ater

ial

outs

ide

thei

rre

latio

n-sh

ipw

ithyo

u.

Con

veyi

ngun

der

any

othe

rci

r-cu

mst

ance

sis

perm

itted

sole

lyun

der

the

cond

ition

sst

ated

be-

low

.Su

blic

ensi

ngis

not

al-

low

ed;

sect

ion

10m

akes

itun

nece

ssar

y.3.

Prot

ectin

gU

sers

’L

egal

Rig

hts

From

Ant

i-C

ircu

mve

ntio

nL

aw.

No

cove

red

wor

ksh

all

bede

emed

part

ofan

effe

ctiv

ete

ch-

nolo

gica

lmea

sure

unde

rany

ap-

plic

able

law

fulfi

lling

oblig

a-

tions

unde

rar

ticle

11of

the

WIP

Oco

pyri

ght

trea

tyad

opte

don

20D

ecem

ber

1996

,or

sim

-ila

rla

ws

proh

ibiti

ngor

rest

rict

-in

gci

rcum

vent

ion

ofsu

chm

ea-

sure

s.

Whe

nyo

uco

nvey

aco

vere

dw

ork,

you

wai

vean

yle

gal

pow

erto

forb

idci

rcum

vent

ion

ofte

chno

logi

calm

easu

res

toth

eex

tent

such

circ

umve

ntio

nis

ef-

fect

edby

exer

cisi

ngri

ghts

un-

der

this

Lic

ense

with

resp

ectt

oth

eco

vere

dw

ork,

and

you

dis-

clai

man

yin

tent

ion

tolim

itop

-er

atio

nor

mod

ifica

tion

ofth

ew

ork

asa

mea

nsof

enfo

rcin

g,ag

ains

tthe

wor

k’s

user

s,yo

uror

thir

dpa

rtie

s’le

gal

righ

tsto

for-

bid

circ

umve

ntio

nof

tech

nolo

g-ic

alm

easu

res.

4.C

onve

ying

Ver

batim

Cop

ies.

You

may

conv

eyve

rbat

imco

pies

ofth

ePr

ogra

m’s

sour

ceco

deas

you

rece

ive

it,in

any

med

ium

,pro

vide

dth

atyo

uco

n-sp

icuo

usly

and

appr

opri

atel

ypu

blis

hon

each

copy

anap

pro-

pria

teco

pyri

ght

notic

e;ke

epin

tact

alln

otic

esst

atin

gth

atth

isL

icen

sean

dan

yno

n-pe

rmis

sive

term

sad

ded

inac

cord

with

sec-

tion

7ap

ply

toth

eco

de;

keep

inta

ctal

lnot

ices

ofth

eab

senc

eof

any

war

rant

y;an

dgi

veal

lre

cipi

ents

aco

pyof

this

Lic

ense

alon

gw

ithth

ePr

ogra

m.

You

may

char

gean

ypr

ice

orno

pric

efo

reac

hco

pyth

atyo

uco

n-ve

y,an

dyo

um

ayof

fer

supp

ort

orw

arra

nty

prot

ectio

nfo

ra

fee.

5.C

onve

ying

Mod

ified

Sour

ceV

ersi

ons.

You

may

conv

eya

wor

kba

sed

onth

ePr

ogra

m,o

rthe

mod

ifica

-tio

nsto

prod

uce

itfr

omth

ePr

o-gr

am,i

nth

efo

rmof

sour

ceco

deun

dert

hete

rmso

fsec

tion

4,pr

o-vi

ded

that

you

also

mee

tal

lof

thes

eco

nditi

ons:

*a)

The

wor

km

ustc

arry

prom

i-ne

ntno

tices

stat

ing

that

you

mod

ified

it,an

dgi

ving

are

le-

vant

date

.*

b)T

hew

ork

mus

tca

rry

prom

inen

tno

tices

stat

ing

that

itis

rele

ased

unde

rth

isL

i-ce

nse

and

any

cond

ition

sad

ded

unde

rse

ctio

n7.

Thi

sre

quir

e-m

ent

mod

ifies

the

requ

irem

ent

inse

ctio

n4

to“k

eep

inta

ctal

lno

tices

”.*

c)Y

oum

ustl

icen

seth

een

tire

wor

k,as

aw

hole

,un-

der

this

Lic

ense

toan

yone

who

com

esin

topo

sses

sion

ofa

copy

.T

his

Lic

ense

will

ther

efor

eap

-pl

y,al

ong

with

any

appl

icab

lese

ctio

n7

addi

tiona

lte

rms,

toth

ew

hole

ofth

ew

ork,

and

all

itspa

rts,

rega

rdle

ssof

how

they

are

pack

aged

.T

his

Lic

ense

give

sno

perm

issi

onto

licen

seth

ew

ork

inan

yot

her

way

,bu

tit

does

not

inva

lidat

esu

chpe

r-m

issi

onif

you

have

sepa

rate

lyre

ceiv

edit.

*d)

Ifth

ew

ork

has

inte

ract

ive

user

inte

rfac

es,e

ach

mus

tdis

play

App

ropr

iate

Leg

alN

otic

es;

how

ever

,if

the

Pro-

gram

has

inte

ract

ive

inte

rfac

esth

atdo

not

disp

lay

App

ropr

iate

Leg

alN

otic

es,

your

wor

kne

edno

tmak

eth

emdo

so.

Aco

mpi

latio

nof

aco

vere

dw

ork

with

othe

rsep

arat

ean

din

-de

pend

entw

orks

,whi

char

eno

tby

thei

rnat

ure

exte

nsio

nsof

the

cove

red

wor

k,an

dw

hich

are

notc

ombi

ned

with

itsu

chas

tofo

rma

larg

erpr

ogra

m,i

nor

ona

volu

me

ofa

stor

age

ordi

stri

-bu

tion

med

ium

,is

calle

dan

“ag-

greg

ate”

ifth

eco

mpi

latio

nan

dits

resu

lting

copy

righ

tar

eno

tus

edto

limit

the

acce

ssor

le-

gal

righ

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the

com

pila

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sus

ers

beyo

ndw

hat

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indi

vid-

ual

wor

kspe

rmit.

Incl

usio

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aco

vere

dw

ork

inan

aggr

egat

edo

esno

tca

use

this

Lic

ense

toap

ply

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eot

her

part

sof

the

aggr

egat

e.6.

Con

veyi

ngN

on-

Sour

ceFo

rms.

You

may

conv

eya

cove

red

wor

kin

obje

ctco

defo

rmun

-de

rth

ete

rms

ofse

ctio

ns4

and

5,pr

ovid

edth

atyo

ual

soco

n-ve

yth

em

achi

ne-r

eada

ble

Cor

-re

spon

ding

Sour

ceun

der

the

term

sof

this

Lic

ense

,in

one

ofth

ese

way

s:

*a)

Con

vey

the

obje

ctco

dein

,or

embo

died

in,

aph

ysic

alpr

oduc

t(i

nclu

ding

aph

ysic

aldi

stri

butio

nm

ediu

m),

acco

m-

pani

edby

the

Cor

resp

ondi

ngSo

urce

fixed

ona

dura

ble

phys

-ic

alm

ediu

mcu

stom

arily

used

for

soft

war

ein

terc

hang

e.*

b)C

onve

yth

eob

ject

code

in,

orem

bodi

edin

,a

phys

ical

prod

-uc

t(i

nclu

ding

aph

ysic

aldi

stri

-bu

tion

med

ium

),ac

com

pani

edby

aw

ritte

nof

fer,

valid

for

atle

astt

hree

year

san

dva

lidfo

ras

long

asyo

uof

fer

spar

epa

rts

orcu

stom

ersu

ppor

tfo

rth

atpr

od-

uct

mod

el,

togi

vean

yone

who

poss

esse

sth

eob

ject

code

eith

er

(1)

aco

pyof

the

Cor

resp

ond-

ing

Sour

cefo

ral

lth

eso

ftw

are

inth

epr

oduc

ttha

tis

cove

red

byth

isL

icen

se,o

na

dura

ble

phys

-ic

alm

ediu

mcu

stom

arily

used

for

soft

war

ein

terc

hang

e,fo

ra

pric

eno

mor

eth

anyo

urre

ason

-ab

leco

stof

phys

ical

lype

rfor

m-

ing

this

conv

eyin

gof

sour

ce,

or(2

)ac

cess

toco

pyth

eC

or-

resp

ondi

ngSo

urce

from

ane

t-w

ork

serv

erat

noch

arge

.*

c)C

onve

yin

divi

dual

copi

esof

the

obje

ctco

dew

itha

copy

ofth

ew

ritte

nof

fer

topr

ovid

eth

eC

or-

resp

ondi

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urce

.Thi

salte

rna-

tive

isal

low

edon

lyoc

casi

onal

lyan

dno

ncom

mer

cial

ly,a

ndon

lyif

you

rece

ived

the

obje

ctco

dew

ithsu

chan

offe

r,in

acco

rdw

ithsu

bsec

tion

6b.

*d)

Con

-ve

yth

eob

ject

code

byof

feri

ngac

cess

from

ade

sign

ated

plac

e(g

ratis

orfo

ra

char

ge),

and

of-

fer

equi

vale

ntac

cess

toth

eC

or-

resp

ondi

ngSo

urce

inth

esa

me

way

thro

ugh

the

sam

epl

ace

atno

furt

her

char

ge.

You

need

not

requ

ire

reci

pien

tsto

copy

the

Cor

resp

ondi

ngSo

urce

alon

gw

ithth

eob

ject

code

.Ift

hepl

ace

toco

pyth

eob

ject

code

isa

netw

ork

serv

er,t

heC

orre

spon

d-in

gSo

urce

may

beon

adi

ffer

-

ents

erve

r(op

erat

edby

you

ora

thir

dpa

rty)

that

supp

orts

equi

va-

lent

copy

ing

faci

litie

s,pr

ovid

edyo

um

aint

ain

clea

rdi

rect

ions

next

toth

eob

ject

code

sayi

ngw

here

tofin

dth

eC

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spon

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urce

.R

egar

dles

sof

wha

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rver

host

sth

eC

orre

spon

ding

Sour

ce,

you

rem

ain

oblig

ated

toen

sure

that

itis

avai

labl

efo

ras

long

asne

eded

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tisfy

thes

ere

quir

emen

ts.

*e)

Con

-ve

yth

eob

ject

code

usin

gpe

er-

to-p

eer

tran

smis

sion

,pr

ovid

edyo

uin

form

othe

rpe

ers

whe

reth

eob

ject

code

and

Cor

resp

ond-

ing

Sour

ceof

the

wor

kar

ebe

ing

offe

red

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ege

nera

lpu

blic

atno

char

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ders

ubse

ctio

n6d

.

Ase

para

ble

port

ion

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eob

-je

ctco

de,w

hose

sour

ceco

deis

excl

uded

from

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Cor

resp

ond-

ing

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ceas

aSy

stem

Lib

rary

,ne

edno

tbe

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uded

inco

nvey

-in

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eob

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k.

A“U

ser

Prod

uct”

isei

ther

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a“c

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mer

prod

uct”

,w

hich

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nsan

yta

ngib

lepe

rson

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oper

tyw

hich

isno

rmal

lyus

edfo

rpe

rson

al,

fam

ily,

orho

use-

hold

purp

oses

,or

(2)

anyt

hing

desi

gned

orso

ldfo

rin

corp

ora-

tion

into

adw

ellin

g.In

de-

term

inin

gw

heth

era

prod

uct

isa

cons

umer

prod

uct,

doub

tful

case

ssh

all

bere

solv

edin

favo

rof

cove

rage

.Fo

ra

part

icul

arpr

oduc

tre

ceiv

edby

apa

rtic

u-la

rus

er,“

norm

ally

used

”re

fers

toa

typi

cal

orco

mm

onus

eof

that

clas

sof

prod

uct,

rega

rdle

ssof

the

stat

usof

the

part

icul

arus

eror

ofth

ew

ayin

whi

chth

epa

rtic

ular

user

actu

ally

uses

,or

expe

cts

oris

expe

cted

tous

e,th

epr

oduc

t.A

prod

uct

isa

cons

umer

prod

uct

rega

rdle

ssof

whe

ther

the

prod

ucth

assu

bsta

n-tia

lco

mm

erci

al,

indu

stri

alor

non-

cons

umer

uses

,unl

ess

such

uses

repr

esen

tth

eon

lysi

gnifi

-ca

ntm

ode

ofus

eof

the

prod

uct.

“Ins

talla

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Info

rmat

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for

aU

ser

Prod

uct

mea

nsan

ym

eth-

ods,

proc

edur

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auth

oriz

atio

nke

ys,

orot

her

info

rmat

ion

re-

quir

edto

inst

all

and

exec

ute

mod

ified

vers

ions

ofa

cove

red

wor

kin

that

Use

rPr

oduc

tfro

ma

mod

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Cor

-re

spon

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Sour

ce.

The

info

r-m

atio

nm

ust

suffi

ceto

ensu

reth

atth

eco

ntin

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ngof

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mod

ified

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inno

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ente

dor

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r-

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dw

ithso

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use

mod

-ifi

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nha

sbe

enm

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Ifyo

uco

nvey

anob

ject

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kun

der

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in,

orw

ith,

orsp

ecifi

cally

for

use

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ser

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ey-

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ansf

erre

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reci

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urce

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der

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acco

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utth

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are

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icly

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enta

tion

avai

labl

eto

the

publ

icin

sour

ceco

defo

rm),

and

mus

tre

quir

eno

spec

ial

pass

wor

dor

key

for

unpa

ckin

g,re

adin

gor

copy

ing.

7.A

dditi

onal

Term

s.

“Add

ition

alpe

rmis

sion

s”ar

ete

rms

that

supp

lem

entt

hete

rms

ofth

isL

icen

seby

mak

ing

exce

ptio

nsfr

omon

eor

mor

eof

itsco

nditi

ons.

Add

ition

alpe

rmis

sion

sth

atar

eap

plic

able

toth

een

tire

Prog

ram

shal

lbe

trea

ted

asth

ough

they

wer

ein

clud

edin

this

Lic

ense

,to

the

exte

ntth

atth

eyar

eva

lidun

der

appl

icab

lela

w.

Ifad

ditio

nal

perm

issi

ons

appl

yon

lyto

part

ofth

ePr

ogra

m,

that

part

may

beus

edse

para

tely

unde

rth

ose

perm

issi

ons,

but

the

entir

ePr

ogra

mre

mai

nsgo

vern

edby

this

Lic

ense

with

out

rega

rdto

the

addi

tiona

lper

mis

sion

s.

Whe

nyo

uco

nvey

aco

pyof

aco

vere

dw

ork,

you

may

atyo

urop

tion

rem

ove

any

addi

tiona

lpe

rmis

sion

sfr

omth

atco

py,

orfr

oman

ypa

rtof

it.(A

ddi-

tiona

lpe

rmis

sion

sm

aybe

wri

t-te

nto

requ

ire

thei

row

nre

mov

alin

cert

ain

case

sw

hen

you

mod

-if

yth

ew

ork.

)Y

oum

aypl

ace

addi

tiona

lper

mis

sion

son

mat

e-ri

al,a

dded

byyo

uto

aco

vere

dw

ork,

forw

hich

you

have

orca

ngi

veap

prop

riat

eco

pyri

ght

per-

mis

sion

.

Not

with

stan

ding

any

othe

rpr

o-vi

sion

ofth

isL

icen

se,f

orm

ate-

rial

you

add

toa

cove

red

wor

k,yo

um

ay(i

fau

thor

ized

byth

eco

pyri

ght

hold

ers

ofth

atm

ate-

rial

)su

pple

men

tth

ete

rms

ofth

isL

icen

sew

ithte

rms:

*a)

Dis

clai

min

gw

arra

nty

orlim

iting

liabi

lity

diff

eren

tlyfr

omth

ete

rms

ofse

ctio

ns15

and

16of

this

Lic

ense

;or

*b)

Req

uiri

ngpr

eser

vatio

nof

spec

-ifi

edre

ason

able

lega

lno

tices

orau

thor

attr

ibut

ions

inth

atm

ater

ial

orin

the

App

ropr

iate

Leg

alN

otic

esdi

spla

yed

byw

orks

cont

aini

ngit;

or*

c)Pr

ohib

iting

mis

repr

esen

tatio

nof

the

orig

inof

that

mat

eria

l,or

requ

irin

gth

atm

odifi

edve

rsio

nsof

such

mat

eria

lbe

mar

ked

inre

ason

able

way

sas

diff

eren

tfr

omth

eor

igin

alve

rsio

n;or

*d)

Lim

iting

the

use

forp

ublic

itypu

rpos

esof

nam

esof

licen

sors

orau

thor

sof

the

mat

eria

l;or

*e)

Dec

linin

gto

gran

tri

ghts

unde

rtr

adem

ark

law

for

use

ofso

me

trad

ena

mes

,tr

adem

arks

,or

serv

ice

mar

ks;o

r*f)

Req

uir-

ing

inde

mni

ficat

ion

oflic

enso

rsan

dau

thor

sof

that

mat

eria

lby

anyo

new

hoco

nvey

sth

em

ate-

rial

(or

mod

ified

vers

ions

ofit)

with

cont

ract

uala

ssum

ptio

nsof

liabi

lity

toth

ere

cipi

ent,

for

any

liabi

lity

that

thes

eco

ntra

ctua

las

sum

ptio

nsdi

rect

lyim

pose

onth

ose

licen

sors

and

auth

ors.

All

othe

rno

n-pe

rmis

sive

ad-

ditio

nal

term

sar

eco

nsid

ered

“fur

ther

rest

rict

ions

”w

ithin

the

mea

ning

ofse

ctio

n10

.If

the

Prog

ram

asyo

ure

ceiv

edit,

oran

ypa

rtof

it,co

ntai

nsa

notic

est

atin

gth

atit

isgo

vern

edby

this

Lic

ense

alon

gw

itha

term

that

isa

furt

her

rest

rict

ion,

you

may

rem

ove

that

term

.If

alic

ense

docu

men

tco

ntai

nsa

furt

her

re-

stri

ctio

nbu

tper

mits

relic

ensi

ngor

conv

eyin

gun

dert

his

Lic

ense

,yo

um

ayad

dto

aco

vere

dw

ork

mat

eria

lgo

vern

edby

the

term

sof

that

licen

sedo

cum

ent,

pro-

vide

dth

atth

efu

rthe

rre

stri

ctio

ndo

esno

tsu

rviv

esu

chre

licen

s-in

gor

conv

eyin

g.

Ifyo

uad

dte

rms

toa

cove

red

wor

kin

acco

rdw

ithth

isse

ctio

n,yo

um

ust

plac

e,in

the

rele

vant

sour

cefil

es,

ast

atem

ent

ofth

ead

ditio

nal

term

sth

atap

ply

toth

ose

files

,or

ano

tice

indi

cat-

ing

whe

reto

find

the

appl

icab

lete

rms.

Add

ition

alte

rms,

perm

issi

veor

non-

perm

issi

ve,

may

best

ated

inth

efo

rmof

ase

para

tely

wri

t-te

nlic

ense

,or

stat

edas

exce

p-tio

ns;

the

abov

ere

quir

emen

tsap

ply

eith

erw

ay.

8.Te

rmin

a-tio

n.

You

may

notp

ropa

gate

orm

od-

ify

aco

vere

dw

ork

exce

ptas

ex-

pres

sly

prov

ided

unde

rth

isL

i-ce

nse.

Any

atte

mpt

othe

rwis

e

topr

opag

ate

orm

odif

yit

isvo

id,a

ndw

illau

tom

atic

ally

ter-

min

ate

your

righ

tsun

dert

his

Li-

cens

e(i

nclu

ding

any

pate

ntli-

cens

esgr

ante

dun

der

the

thir

dpa

ragr

aph

ofse

ctio

n11

).

How

ever

,if

you

ceas

eal

lvio

la-

tion

ofth

isL

icen

se,

then

your

licen

sefr

oma

part

icul

arco

py-

righ

thol

deri

sre

inst

ated

(a)p

ro-

visi

onal

ly,

unle

ssan

dun

tilth

eco

pyri

ght

hold

erex

plic

itly

and

final

lyte

rmin

ates

your

licen

se,

and

(b)p

erm

anen

tly,i

fthe

copy

-ri

ght

hold

erfa

ilsto

notif

yyo

uof

the

viol

atio

nby

som

ere

ason

-ab

lem

eans

prio

rto

60da

ysaf

ter

the

cess

atio

n.

Mor

eove

r,yo

urlic

ense

from

apa

rtic

ular

copy

righ

thol

deri

sre

-in

stat

edpe

rman

ently

ifth

eco

py-

righ

tho

lder

notifi

esyo

uof

the

viol

atio

nby

som

ere

ason

able

mea

ns,t

his

isth

efir

sttim

eyo

uha

vere

ceiv

edno

tice

ofvi

olat

ion

ofth

isL

icen

se(f

oran

yw

ork)

from

that

copy

righ

tho

lder

,and

you

cure

the

viol

atio

npr

ior

to30

days

afte

ryou

rrec

eipt

ofth

eno

tice.

Term

inat

ion

ofyo

urri

ghts

unde

rth

isse

ctio

ndo

esno

tte

rmin

ate

the

licen

ses

ofpa

rtie

sw

hoha

vere

ceiv

edco

pies

orri

ghts

from

you

unde

rth

isL

icen

se.

Ifyo

urri

ghts

have

been

term

inat

edan

dno

tper

man

ently

rein

stat

ed,y

oudo

not

qual

ify

tore

ceiv

ene

wlic

ense

sfo

rth

esa

me

mat

eria

lun

der

sect

ion

10.

9.A

ccep

-ta

nce

Not

Req

uire

dfo

rH

avin

gC

opie

s.

You

are

not

requ

ired

toac

-ce

ptth

isL

icen

sein

orde

rto

rece

ive

orru

na

copy

ofth

ePr

ogra

m.

Anc

illar

ypr

opag

a-tio

nof

aco

vere

dw

ork

occu

r-ri

ngso

lely

asa

cons

eque

nce

ofus

ing

peer

-to-

peer

tran

smis

sion

tore

ceiv

ea

copy

likew

ise

does

not

requ

ire

acce

ptan

ce.

How

-ev

er,n

othi

ngot

her

than

this

Li-

cens

egr

ants

you

perm

issi

onto

prop

agat

eor

mod

ify

any

cov-

ered

wor

k.T

hese

actio

nsin

-fr

inge

copy

righ

tif

you

dono

tac

cept

this

Lic

ense

.T

here

fore

,by

mod

ifyi

ngor

prop

agat

ing

aco

vere

dw

ork,

you

indi

cate

your

acce

ptan

ceof

this

Lic

ense

todo

so.

10.

Aut

omat

icL

icen

sing

ofD

owns

trea

mR

ecip

ient

s.

Eac

htim

eyo

uco

nvey

aco

vere

dw

ork,

the

reci

pien

tau

tom

ati-

cally

rece

ives

alic

ense

from

the

orig

inal

licen

sors

,to

run,

mod

-if

yan

dpr

opag

ate

that

wor

k,su

b-je

ctto

this

Lic

ense

.You

are

not

resp

onsi

ble

for

enfo

rcin

gco

m-

plia

nce

byth

ird

part

ies

with

this

Lic

ense

.

An

“ent

itytr

ansa

ctio

n”is

atr

ansa

ctio

ntr

ansf

erri

ngco

ntro

lof

anor

gani

zatio

n,or

subs

tan-

tially

alla

sset

sof

one,

orsu

bdi-

vidi

ngan

orga

niza

tion,

orm

erg-

ing

orga

niza

tions

.If

prop

aga-

tion

ofa

cove

red

wor

kre

sults

from

anen

tity

tran

sact

ion,

each

part

yto

that

tran

sact

ion

who

re-

ceiv

esa

copy

ofth

ew

ork

also

rece

ives

wha

teve

rlic

ense

sto

the

wor

kth

epa

rty’

spr

edec

esso

rin

inte

rest

had

orco

uld

give

unde

rth

epr

evio

uspa

ragr

aph,

plus

ari

ght

topo

sses

sion

ofth

eC

or-

resp

ondi

ngSo

urce

ofth

ew

ork

from

the

pred

eces

sori

nin

tere

st,

ifth

epr

edec

esso

rha

sit

orca

nge

titw

ithre

ason

able

effo

rts.

You

may

not

impo

sean

yfu

r-th

erre

stri

ctio

nson

the

exer

cise

ofth

eri

ghts

gran

ted

oraf

firm

edun

der

this

Lic

ense

.Fo

rex

-

ampl

e,yo

um

ayno

tim

pose

alic

ense

fee,

roya

lty,

orot

her

char

gefo

rex

erci

seof

righ

tsgr

ante

dun

der

this

Lic

ense

,and

you

may

not

initi

ate

litig

a-tio

n(i

nclu

ding

acr

oss-

clai

mor

coun

terc

laim

ina

law

suit)

alle

g-in

gth

atan

ypa

tent

clai

mis

in-

frin

ged

bym

akin

g,us

ing,

sell-

ing,

offe

ring

for

sale

,or

impo

rt-

ing

the

Prog

ram

oran

ypo

rtio

nof

it.11

.Pat

ents

.

A“c

ontr

ibut

or”

isa

copy

righ

tho

lder

who

auth

oriz

esus

eun

der

this

Lic

ense

ofth

ePr

ogra

mor

aw

ork

onw

hich

the

Prog

ram

isba

sed.

The

wor

kth

uslic

ense

dis

calle

dth

eco

ntri

buto

r’s

“con

-tr

ibut

orve

rsio

n”.

Aco

ntri

buto

r’s

“ess

entia

lpat

ent

clai

ms”

are

all

pate

ntcl

aim

sow

ned

orco

ntro

lled

byth

eco

n-tr

ibut

or,

whe

ther

alre

ady

ac-

quir

edor

here

afte

rac

quir

ed,

that

wou

ldbe

infr

inge

dby

som

em

anne

r,pe

rmitt

edby

this

Li-

cens

e,of

mak

ing,

usin

g,or

sell-

ing

itsco

ntri

buto

rve

rsio

n,bu

tdo

noti

nclu

decl

aim

stha

twou

ldbe

infr

inge

don

lyas

aco

nse-

quen

ceof

furt

her

mod

ifica

tion

ofth

eco

ntri

buto

rve

rsio

n.Fo

r

purp

oses

ofth

isde

finiti

on,“

con-

trol

”in

clud

esth

eri

ght

togr

ant

pate

ntsu

blic

ense

sin

am

anne

rco

nsis

tent

with

the

requ

irem

ents

ofth

isL

icen

se.

Eac

hco

ntri

buto

rgr

ants

you

ano

n-ex

clus

ive,

wor

ldw

ide,

roya

lty-f

ree

pate

ntlic

ense

un-

der

the

cont

ribu

tor’

ses

sent

ial

pate

ntcl

aim

s,to

mak

e,us

e,se

ll,of

fer

for

sale

,im

port

and

othe

r-w

ise

run,

mod

ify

and

prop

agat

eth

eco

nten

tsof

itsco

ntri

buto

rve

rsio

n.

Inth

efo

llow

ing

thre

epa

ra-

grap

hs,

a“p

aten

tlic

ense

”is

any

expr

ess

agre

emen

tor

com

-m

itmen

t,ho

wev

erde

nom

inat

ed,

nott

oen

forc

ea

pate

nt(s

uch

asan

expr

ess

perm

issi

onto

prac

-tic

ea

pate

ntor

cove

nant

not

tosu

efo

rpat

enti

nfri

ngem

ent)

.To

“gra

nt”

such

apa

tent

licen

seto

apa

rty

mea

nsto

mak

esu

chan

agre

emen

tor

com

mitm

ent

not

toen

forc

ea

pate

ntag

ains

tth

epa

rty.

Ifyo

uco

nvey

aco

vere

dw

ork,

know

ingl

yre

lyin

gon

apa

tent

licen

se,

and

the

Cor

resp

ondi

ngSo

urce

ofth

ew

ork

isno

tava

il-

able

for

anyo

neto

copy

,fr

eeof

char

gean

dun

der

the

term

sof

this

Lic

ense

,th

roug

ha

pub-

licly

avai

labl

ene

twor

kse

rver

orot

her

read

ilyac

cess

ible

mea

ns,

then

you

mus

tei

ther

(1)

caus

eth

eC

orre

spon

ding

Sour

ceto

beso

avai

labl

e,or

(2)

arra

nge

tode

priv

eyo

urse

lfof

the

bene

fitof

the

pate

ntlic

ense

for

this

part

icul

arw

ork,

or(3

)ar

rang

e,in

am

anne

rco

nsis

tent

with

the

requ

irem

ents

ofth

isL

icen

se,

toex

tend

the

pate

ntlic

ense

todo

wns

trea

mre

cipi

ents

.“K

now

-in

gly

rely

ing”

mea

nsyo

uha

veac

tual

know

ledg

eth

at,

but

for

the

pate

ntlic

ense

,you

rco

nvey

-in

gth

eco

vere

dw

ork

ina

coun

-tr

y,or

your

reci

pien

t’sus

eof

the

cove

red

wor

kin

aco

untr

y,w

ould

infr

inge

one

orm

ore

iden

-tifi

able

pate

nts

inth

atco

untr

yth

atyo

uha

vere

ason

tobe

lieve

are

valid

.

If,p

ursu

ant

toor

inco

nnec

tion

with

asi

ngle

tran

sact

ion

orar

-ra

ngem

ent,

you

conv

ey,o

rpro

p-ag

ate

bypr

ocur

ing

conv

eyan

ceof

,aco

vere

dw

ork,

and

gran

tapa

tent

licen

seto

som

eof

the

par-

ties

rece

ivin

gth

eco

vere

dw

ork

auth

oriz

ing

them

tous

e,pr

op-

agat

e,m

odif

yor

conv

eya

spe-

cific

copy

ofth

eco

vere

dw

ork,

then

the

pate

ntlic

ense

you

gran

tis

auto

mat

ical

lyex

tend

edto

all

reci

pien

tsof

the

cove

red

wor

kan

dw

orks

base

don

it.

Apa

tent

licen

seis

“dis

crim

i-na

tory

”if

itdo

esno

tin

clud

ew

ithin

the

scop

eof

itsco

vera

ge,

proh

ibits

the

exer

cise

of,

oris

cond

ition

edon

the

non-

exer

cise

ofon

eor

mor

eof

the

righ

tsth

atar

esp

ecifi

cally

gran

ted

unde

rth

isL

icen

se.

You

may

notc

on-

vey

aco

vere

dw

ork

ifyo

uar

ea

part

yto

anar

rang

emen

tw

itha

thir

dpa

rty

that

isin

the

busi

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