CIS192 Python Programming - Introductioncis192/fall2015/files/lec/lec1.pdf · PyDev for Eclipse...

CIS192 Python ProgrammingIntroduction

Robert Rand

University of Pennsylvania

August 27, 2015

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Outline

1 LogisticsGradingOffice HoursShared LectureSoftware

2 PythonWhat is PythonThe BasicsDynamic Types

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Grading

Homeworks: 65% of grade.Final Project: 30% of grade.Participation: 5% of grade.

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Homework

Due Sunday at midnight, ten days after classOne late weekCan discuss with a partnerCode must be your ownCite partner / all references usedSubmit via Canvas

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Final Project

Work with up to one partnerProposal due Nov 8thDemo ready version due last day of classFinal version due last day of exams

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Office Hours

Instructor: Robert RandI Thursday 1:30 - 3:30pm, Levine 513

TA: Joseph CappadonaI Tuesday 3:00 - 5:00pm, DRL 4E9

TA: Raymond YinI Friday 3:00 - 5:00pm, Towne 303

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Shared Lecture

Class: CIS 19X Shared LectureI Room: Towne 100I Time: Tuesdays 6:00 - 7:30I Only a few meetings per semesterI Includes Unix skills, version control

Instructor: Swapneel Sheth

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Programming Environment

PyDev for Eclipse RecommendedI Emacs is also good

Make sure your editor interprets TAB as fourspaces

I Python is whitespace-sensitive!

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Piazza

Use Piazza to find project partners and discusslectures/homeworks with your peers.

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Outline

1 LogisticsGradingOffice HoursShared LectureSoftware

2 PythonWhat is PythonThe BasicsDynamic Types

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Easy to Learn

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Easy to Use

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Easy to Abuse

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REPL

Read Evaluate Print LoopType “Python” at the terminalTest out language behavior hereGet information with dir(), help(), type()

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2.7 vs. 3.4

Python 2.7 Python 3.4print “hello world!” print(“hello world!”)1/2 = 0 1/2 = 0.5

1 // 2 = 0No Unicode support Unicode supportMore popular Gaining popularityBetter library support Good library support

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Solution

from __future__ importabsolute_import, division,print_function

Changes Python 2.7’s behavior to mimic 3.x’sBest of both worldsAdd to the top of every .py file.

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Static Types

What are static types?A form of integrated specificationEnforced at compile time.VerbosePython does not have these.

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Untyped?

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Dynamic Types

Basically a system of tags.Let’s see how they work in practice.

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Identifiers, Names, Variables

All 3 mean the same thing[A-Za-z0-9_] First character cannot be a numberVariable naming convention

I Functions and variables: lower_with_underscoreI Constants: UPPER_WITH_UNDERSCORE

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Binding

x = 1y = xx = ’a’

X 1

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Binding

x = 1y = xx = ’a’

X

Y

1

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Binding

x = 1y = xx = ’a’

X

Y

1

a

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Types

Every object has a typeInspect types with type(object)

isinstance(object, type) checks typeheirarchyTypes can be compared for equality but usuallywant isinstance()Some types:

I int, float, complexI str, bytes, tupleI list,bytearrayI range, bool, NoneI function

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Objects

Python treats all data as objectsIdentity

I Memory addressI Does not change

TypeI Does not change

ValueI Mutable → [1,2]I Immutable → (1,2)

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Math

LiteralsI Integers: 1, 2I Floats: 1.0, 2e10I Complex: 1j, 2e10jI Binary: 0b1001, Hex: 0xFF, Octal: 0o72

OperationsI Arithmetic: + - * /I Power: **I Integer division: //I Modulus: %I Bitwise: « » & | ˆI Comparison: <, >, <=, >=, ==, !=

Assignment OperatorsI += *= /= &= ...I No ++ or --

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Strings

Can use either single or double quotesUse single to show double flip-flop "’" → ’ and ’"’→ "Triplequote for multiline stringCan concat strings by sepating string literals withwhitespaceAll strings are unicodePrefixing with r means raw. No need to escape:r’\n’

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Conditionals

One if blockZero or more elif blocksZero or one else blockBooleans: True False

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Sequences

ImmutableI Strings, Tuples, Bytes

MutableI Lists, Byte Arrays

OperationsI len()I IndexingI SlicingI inI not in

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Range

Immutable sequence of numbersrange(stop), range(start,stop)range(start,stop,step])

start defaults to 0step defaults to 1All numbers in [start,stop) by incrementing start bystepNegative steps are validMemory efficent: Calculates values as you iterateover them

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Loops

For each loopsI Iterate over an object

While loopsI Continues as long as condition holds

BothI else: executes after loop finishesI break: stops the loop and skips the else clauseI continue: starts the next iteration of the loop

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Functions

Functions are first classI Can pass them as argumentsI Can assign them to variables

Define functions with a defreturn keyword to return a valueIf a function reaches the end of the block withoutreturningIt will return None (null)

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Imports

Allow use of other python files and librariesimports: import math

Named imports: import math as m

Specific imports: from math import pow

Import all: from math import *

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