cis192 python programming - introductioncis192/spring2016/files/lec/lec1.pdf · cis192 python...

CIS192 Python ProgrammingIntroduction

Dan Gillis

University of Pennsylvania

January 20th, 2016

Dan Gillis (University of Pennsylvania) CIS 192 January 20th, 2016 1 / 37

Outline

1 About this CoursePeopleCurriculum

2 LogisticsGradingOffice HoursSoftware

3 PythonWhat is PythonThe BasicsDynamic Types


People

Instructor: Robert Rand

TAs: Adel Qalieh, Dan Gillis, Harry Smith


What are CIS 110-121?

Core computer science courses at Penn.Teach fundamentals of programming and criticalconcepts like recursion and data structures.Much more important than this course.But maybe less fun.


What is CIS 192?

Let’s learn Python!Part One - Python Basics (∼6 weeks)

I How to program in Python.I Enough to add “Python” to your resume.

Part Two - Fun with Python (∼8 weeks)I Cool stuff we can do in Python (eg. Machine Learning,

Web Apps)I Check out previous iterations of course.I Send me ideas (suggestion box is open all semester)


What is the CIS 19x Shared Lecture?

Learn CS skills with Swapneel Seth.Some of these will be used in the course(particularly command line arguments).No homeworkMeets on Tuesdays


Outline





Grading

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


Homework

Due Sunday at midnight, eleven days after classOne “Late Week” extension

I Subsequent late homeworks will be penalized 10%I Homework that is more than one week late will not be

accepted.

Submit via Canvas


Homework

Will be graded for correctness, efficiency andstyle.Correctness: We will often include “test” files forunit testing - use them and add your own tests.Style: Be sure to follow the PEP-8 style guidelines- you can add an automatic checker to most IDEs.Efficiency: Think before coding and try to avoidunbounded recursion and highly nested loops.


Policies

General: Code of Academic IntegrityI http://www.upenn.edu/academicintegrity/ai_codeofacademicintegrity.html

Specifics:I Discuss with up to one partner.I Write your own code.I Do not look up sources that directly solve the problemI Cite partner and sources consulted (if any).


http://www.upenn.edu/academicintegrity/ai_codeofacademicintegrity.html

http://www.upenn.edu/academicintegrity/ai_codeofacademicintegrity.html

Final Project

Work with up to one partnerI You can search for partners on Piazza

Proposal due March 13thFinal Projects due April 27thProject Demos will be scheduled for during thedepartment-wide Demo Day and Reading Days.Start thinking about a project now!


Office Hours

Robert Rand: Friday 2:30 - 4:30pm, Levine 513and by appointment.

I Not including this Friday

Adel Qalieh: Monday 3-5pm, Location TBD.Dan Gillis: Thursday 4-6pm, DRL 4N30Harry Smith: Tuesday 3-5pm, Moore 212


Programming Environment

PyDev for Eclipse RecommendedI Emacs/vim are also goodI Plenty of alternatives for various OSs

Set your editor to interpret tabs as four spacesI Python is whitespace-sensitive


Piazza

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


Outline





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 concatenate strings by sepating string literalswith whitespaceStrings are not unicode

I One of the major differences between Python 2 and Python 3

Prefixing 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

List of numbersI Stores all values in memory

range(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 validAlternate function: xrange

I Immutable sequence of numbersI Memory efficient: Calculates values as you iterate over 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/spring2016/files/lec/lec1.pdf · cis192 python...

Documents