CIS192 Python Programming - Introductioncis192/fall2016/files/lec/lec...IDEs also available: PyDev for Eclipse, PyCharm Set your editor to interpret tabs as four spaces Python is whitespace-sensitive

CIS192 Python ProgrammingIntroduction

Raymond Yin

University of Pennsylvania

August 31, 2016

Raymond Yin (University of Pennsylvania) CIS 192 August 31, 2016 1 / 32

Outline

1 LogisticsRooms and Office HoursGradingClass Materials

2 PythonWhat is Python?The Basics


What’s CIS 192?

CIS 19X courses0.5 Credits eachDesigned to teach practical skills

CIS 192: Python ProgrammingPowerful scripting language used in academia and industrySimple to read and write in

Take this class ifYou have some programming experienceYou are relatively new to Python


CIS 192 Logistics

Class: CIS 192 Python ProgrammingListed as CIS 192 201Room: Towne 303Time: Wednesdays, 12:00 - 1:30pm

Instructor: Raymond YinUndergrad in CS (Not a professor)

TAsHarry SmithAlex Frias


CIS 192 001

Class: CIS 19X Shared LectureRoom: Towne 100Time: Tuesdays, 6:00 - 7:30pmGeneral, useful info: command line intro, Git, overview of theInternet

Instructor: Swapneel Sheth


Outline




Grade Breakdown

Homework: 70%1 per weekProgramming assignments

Final Project: 25%Anything you wantIndividually or in a pair

In Class: 5%Participation/Attendance/Piazza

Late PolicyDrop one homework (lowest grade)


Homeworks

Python 3 (3.42 or latest stable)Submit on Canvas!Graded for correctness (80%) and style (20%)Due Sunday nights at 11:59pmHW1 due next Sunday, September 11Academic Integrity

The Office of Student ConductDon’t copy-paste code from other peopleDon’t have mid-level discussions

High-Level: What are the pros/cons of using Python for X?Low-Level: What is the syntax for decorators?Mid-Level: How did you do HW 1?


Outline




Reading

No text book!Python Official DocumentationIn-class slides and code (available on CIS 192 website)Piazza


Programming Environment

Unix system recommendedUbuntu Virtual Machine / Eniac

EditorCan use anything you want (Sublime Text, Atom, vim, emacs, etc.)IDEs also available: PyDev for Eclipse, PyCharmSet your editor to interpret tabs as four spaces

Python is whitespace-sensitive


Outline




Easy to Learn


Easy to Use


Easy to Abuse


History

Designer: Guido van RossumBenevolent Dictator For Life (BDFL)

Multi-Paradigm: Object-Oriented, Functional, Imperative...Strongly and Dynamically TypedWhitespace delimited blocksGarbage Collected


Philosophy

The Zen of PythonBeautiful is better than uglyExplicit is better than implicitSimple is better than complexComplex is better than complicatedReadability Counts

Other ideasThere should be one obvious way to do itClarity over marginal efficiencyWe’re all consenting adults here


Outline




REPL

Read Evaluate Print Loop (a.k.a. an interpreter)Type “Python” at the terminal

Test out language behavior hereGet information with dir(), help(), type()


Identifiers, Names, Variables

All 3 mean the same thingVariable naming convention

Functions and variables: lower_with_underscoremy_num = 5

Constants: UPPER_WITH_UNDERSCORESECONDS_PER_MINUTE = 60


Binding

x = 1y = xx = ’a’

X 1


Binding

x = 1y = xx = ’a’

X

Y

1


Binding

x = 1y = xx = ’a’

X

Y

1

a


Objects

Python treats all data as objectsIdentity

Memory addressDoes not change

TypeDoes not change

ValueMutable: value can be changed (e.g. [1,2])Immutable: value cannot be changed after creation (e.g. (1,2))

EqualityUse is for referential equality (do x and y point to the same object?)Use == for structural equality (are x and y equal based on object’s__eq__ method?)


Types

Every object has a typeInspect types with type(object)isinstance(object, type) checks type hierarchyTypes can be compared for equality, but you usually wantisinstance

Some types:int, floatstrtuple, list, dictrange, bool, Nonefunction


Math

LiteralsIntegers: 1, 2Floats: 1.0, 2e10Complex: 1j, 2e10jBinary: 0b1001, Hex: 0xFF, Octal: 0o72

OperationsArithmetic: + - * /Power: **Integer division: //Modulus: %Bitwise: « » & | ˆComparison: , =, ==, !=

Assignment Operators+= *= /= &= ...No ++ or --


Booleans

True and FalseBoolean operators: and or notAny object can be tested for truth value for use in conditionals, oras operands of the above Boolean operations."Falsy"

None00.0Any empty string/sequence/collection ([],(), etc.)


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 with whitespaceAll strings are unicodePrefixing with r means raw. No need to escape characters: r’\n’


Conditionals

One if blockZero or more elif blocksZero or one else block


Sequences

ImmutableStrings, Tuples

MutableLists

Operationslen()IndexingSlicinginnot in


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 by stepNegative steps are validMemory efficent: Calculates values as you iterate over them


Loops

For each loops (for item in my_list:)Iterate over an object

While loops (while some_condition:)Continues as long as condition holds

Bothelse: executes after loop finishesbreak: stops the loop and skips the else clausestarts the next iteration of the loop


Functions

Functions are first classThey’re objects, too!Can pass them as argumentsCan assign them to variables

Define functions with a defreturn keyword to return a valueIf a function reaches the end of the block without returning,it will return None (null)


Importing Modules

Allow use of other python files and librariesimports: import mathNamed imports: import math as mSpecific imports: from math import powImport all: from math import *


LogisticsRooms and Office HoursGradingClass Materials

PythonWhat is Python?The Basics

Documents

CIS192 Python Programming - Introductioncis192/fall2016/files/lec/lec...IDEs also available: PyDev for Eclipse, PyCharm Set your editor to interpret tabs as four spaces Python is whitespace-sensitive