Python programming

Introduction to the JES environment and basics of Python

Python

• The programming language we will be using is called Python– http://www.python.org– It’s used by companies like Google, Industrial Light &

Magic, Nextel, and others• The kind of Python we’re using is called Jython

(Java-based Python)– http://www.jython.org

• We’ll be using a specific tool to make Python programming easier, called JES (Jython Environment for Students).– http://coweb.cc.gatech.edu/mediaComp-teach/26

JES - Jython Environment for Students

Program Area

Command Area

Program area- A simple editor for programs

Command area- Interaction with Jython

>>> 5 + 38>>> ‘spam’‘spam’>>> “spam”‘spam’>>> “spam and more spam”‘spam and more spam’>>> ‘spam’ + ‘spam’‘spamspam’

Python interaction through commands

Anything you type in command area is evaluated and its value is displayed

• Example:

prompt

>>> print 5 + 38>>> print ‘spam’spam>>> ‘spam’ + ‘spam’‘spamspam’>>> print ‘spam’ + ‘spam’Spamspam

print displays the value of an expression

• In many cases it makes no difference whether you use print - the result gets displayed anyway.

Note: no quotes!

Command Area Editing

• Up/down arrows walk through command history

• You can edit the line at the bottom– Just put the cursor at the end of the line

before hitting Return/Enter.

Variables are names for data

Example:

a= 3

b= -1

c = 2

x = 0

f = a*x*x + b*x + c

Variables -more examples

• Variables of other typesnewsItem = “You’ve got spam!”

• Variables keep their value for the duration of a program or until they get a new value through a new assignment

a = 3

b = a *2 + 5

a = 0

Up to this point the value of a is still 3, but then it changes to 0

Types of data

• Integernum = -3

• Floating point numberanswer = 62.49

• Characterletter = ‘5’

• Stringnote = “lol jkjk”

Python functions

• Python has a lot of built-in functions for general mathematical manipulation, eg:

• sqrt(4) - computes the square root of 4• ord(‘A’) - computes the ASCII code for

character ‘A’ (i.e., a numeric code)• str(4) – produces a string corresponding to

a numberExample: print (-b+sqrt(b*b - 4*a*c))/2*a

Special JES-Python functions

• JES defines some special functions for media computation

Functions in general

F(a,b)

4

‘a’ F(4, ‘a’)

side-effects

Example: sqrt()

sqrt(a)4 2

side-effects

Example: showInformation()

showInformation(message)message

Pops up a new window displaying the message text

showInformation(message):message: the message to show to the userOpens a message dialog to the user showing information

Exploring more functions

• The JES Functions menu has functions arranged by type - check them out!

• Can you find a function that inputs a number?

• Can you find under what category pickAFile() is listed?

Reading

• Chapters 1, and Sections 2.1-2.4 from “Introduction to Computing and Programming in Python” (up to page 22)