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

CIS192 Python ProgrammingIntroduction

Robert Rand

University of Pennsylvania

August 27, 2015

Robert Rand (University of Pennsylvania) CIS 192 August 27, 2015 1 / 30

Outline

1 LogisticsGradingOffice HoursShared LectureSoftware

2 PythonWhat is PythonThe BasicsDynamic Types


Grading

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


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


Final Project

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


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


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


Programming Environment

PyDev for Eclipse RecommendedI Emacs is also good

Make sure your editor interprets TAB as fourspaces

I Python is whitespace-sensitive!


Piazza

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


Outline

1 LogisticsGradingOffice HoursShared LectureSoftware

2 PythonWhat is PythonThe BasicsDynamic Types


Easy to Learn


Easy to Use


Easy to Abuse


REPL

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


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


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.


Static Types

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


Untyped?


Dynamic Types

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


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


Binding

x = 1y = xx = ’a’

X 1


Binding

x = 1y = xx = ’a’

X

Y

1


Binding

x = 1y = xx = ’a’

X

Y

1

a


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


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)


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 --


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’


Conditionals

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


Sequences

ImmutableI Strings, Tuples, Bytes

MutableI Lists, Byte Arrays

OperationsI len()I IndexingI SlicingI inI not 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 bystepNegative steps are validMemory efficent: Calculates values as you iterateover them


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


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)


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 *


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

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