Python programming Introduction to the JES environment and basics of Python

Python The programming language we will be using is called Python – –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) – We’ll be using a specific tool to make Python programming easier, called JES (Jython Environment for Students). –

JES - Jython Environment for Students Program area - A simple editor for programs Command area - Interaction with Jython

>>> >>> ‘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 >>> 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 types newsItem = “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 Integer num = -3 Floating point number answer = Character letter = ‘5’ String note = “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 number Example: 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 user Opens 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 from “Introduction to Computing and Programming in Python” (up to page 22)