Input: parameters

• Parameters are function inputs
  • They are also local variables inside functions and exist only as long as the function is executing

For example:

def greeter(name):
    print('Hello', name)

greeter('Bob')

Hello Bob

• The variable name is the parameter of the function greeter.
• When greeter is called, the string object Bob is passed as an argument of the function
  • Then, Bob is assigned to the variable name when the code inside greeter is running.

Multiple parameters

import turtle

def draw_square(pen, size):
    for i in range(4):
        pen.forward(size)
        pen.left(90)

t = turtle.Turtle()
draw_square(t, 100)

• Notice that parameters may be called in order
• If we don’t want to follow this order, or we want to specify which parameter receives what, we simply state the names of the parameters:

draw_square(pen=t, size=100)

---

What happens if we don’t specify all the parameters?

import turtle

def draw_square(pen, size):
    for i in range(4):
        pen.forward(size)
        pen.left(90)

t = turtle.Turtle()
draw_square(100)

Preset parameters

• We can pre-specify the values of some parameters by assigning some value to them in the definition
  • This also makes the parameter assignment optional when the function is called: see draw_square(t)
    • The function will run every time as if size=100, unless we say different

import turtle

def draw_square(pen, size=100):
    for i in range(4):
        pen.forward(size)
        pen.left(90)

t = turtle.Turtle()
draw_square(t)