Simple Functions and Names

Sec 9-4Web Design

Objectives

The student will:• Know how to create a simple function in

Python.• Know how to call a function in Python.• Know the rules for “names” in Python

Functions• A function is a piece of code you can use

over and over again– Treat it like a black box

• You pass it (optional) values, it does some work, and it (optionally) returns values

• You “call it”,”invoke it”, or “use it” by using its name and parentheses

• The things you pass it go inside the parentheses– output = function( input )

function

input

output

Functions

• As in any programming language Python has functions.– Functions allows you to modularize your code• Easier to read• Easier to debug• Easy to use over and over

Functions

• The basic syntax for defining a Python function takes the form:

def <FUNCTION NAME>(<PARAMETERS>):<SOMETHING>...<SOMETHING>

Functions

def <FUNCTION NAME>(<PARAMETERS>):<SOMETHING>...<SOMETHING>

• Note that the lines of the function are indented.– The number of spaces that make up the

indentation is not that important as long as they are all the same.

Improper FunctionsThis will not be accepted by Python:

Red bar shows the point of the error

This is acceptable

Python Functions in IDLE• IDLE will automatically indent lines in a

function.– To end the function simple un-indent the line.

• IDLE also uses colors to help the readability of a program:

• Red – Comments• Blue – Function Names• Orange – Python word

Calling (Invoking) a Function

• To call a function you type the function:yoyo()forward()

Rules for Python Names• Some names are reserved by the system and are already

defined. Examples are things like: def, print, if, else, while, for, in, and, or, not, return. These names are built in keywords.

• A name in Python must begin with either an alphabetic letter (a-z or A-Z) or the underscore (i.e. _) and can be followed by any sequence of letters, digits, or underscore letters.

• For example,Vaild:Invalid:

iRobot 2robotsmyRobot Robots-r-cooljitterBugjitterBug2my2centsmy_2_cents

Summary• Functions are defined by:def <FUNCTION NAME>(<PARAMETERS>):

<SOMETHING>...<SOMETHING>

• Functions are called byFUNCTION()

• Function names must begin with either an alphabetic letter (a-z or A-Z) or the underscore (i.e. _) and can be followed by any sequence of letters, digits, or underscore letters.

Rest of Today• Take the code for the octagon and put it in a

function.• Call the function 4 times.• When the function is done show me the

results.