6.1 Functions¶

In Python, a function is a named sequence of statements that belong together
Purpose: organize program into chunks

Syntax:

def name( parameters ):
    statements

In a function definition, the keyword in the header is def, which is followed by the name of the function and some parameters enclosed in parentheses
the parameter list is more specifically known as the formal parameters
When you use a function, you provide values to the formal parameters.
Even if a function call needs no arguments, the parentheses ( )after the function name are required. This can lead to a difficult bug: A function name without the parenthesis is a legal expression referring to the function; for example,printand alex.penup, but they do not call the associated functions.

docstrings¶

If the first thing after the function header is a string (some tools insist that it must be a triple quoted string), it is called a docstring and gets special treatment in Python and in some of the programming tools.
Another way to retrieve this information is to use the interactive interpreter, and enter the expression <function_name>.__doc__, which will retrieve the docstring for the function.
- So the string you write as documentation at the start of a function is retrievable by python tools at runtime.
By convention, Python programmers use docstrings for the key documentation of their functions.

Function Call¶

Defining a new function does not make the function run. To do that we need a function call. This is also known as a function invocation
Function calls contain the name of the function to be executed followed by a list of values in parentheses, called arguments, which are assigned to the parameters in the function definition.

import turtle

# this is the function that will be called
def drawSquare(t, sz):
    """Make turtle t draw a square of with side sz."""

    for i in range(4):
        t.forward(sz)
        t.left(90)

wn = turtle.Screen()          # Set up the window and its attributes
wn.bgcolor("lightgreen")

alex = turtle.Turtle()        # create alex
drawSquare(alex, 50)          # Call the function to draw the square

alex.penup()
alex.goto(100,100)
alex.pendown()

drawSquare(alex,75)           # Call the function again to draw another square

wn.exitonclick()