User-defined functions

Introduction to Functions in Python

Hugo Bowne-Anderson

Instructor

What you will learn:

  • Define functions without parameters

  • Define functions with one parameter

  • Define functions that return a value

  • Later: multiple arguments, multiple return values

Introduction to Functions in Python

Built-in functions

  • str()
x = str(5)

print(x)

'5'

print(type(x))

<class 'str'>
Introduction to Functions in Python

Defining a function

def square():    # <- Function header

    new_value = 4 ** 2    # <- Function body
    print(new_value)

square()

16
Introduction to Functions in Python

Function parameters

def square(value):
    new_value = value ** 2
    print(new_value)

square(4)

16

square(5)

25
Introduction to Functions in Python

Return values from functions

  • Return a value from a function using return
def square(value):
    new_value = value ** 2
    return new_value

num = square(4)

print(num)

16
Introduction to Functions in Python

Docstrings

  • Docstrings describe what your function does

  • Serve as documentation for your function

  • Placed in the immediate line after the function header

  • In between triple double quotes """

def square(value):
    """Returns the square of a value."""
    new_value = value ** 2
    return new_value
Introduction to Functions in Python

Let's practice!

Introduction to Functions in Python

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