To group sets of code you can use functions. Functions are small parts of repeatable code.
A function accepts parameters.

Without functions we only have a long list of instructions. Functions can help you organize code. Functions can also be reused, often they are included in modules.

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Example

Functions

Functions can be seen as executable code blocks. A function can be used once or more.

A simple example of a function is:

def currentYear():
print('2018')

currentYear()

The function is immediately called in this example. Function definitions always start with the def keyword.

Functions can be reusable, once created a function can be used in multiple programs. The print function is an example of that.

Functions with parameters

In the example below we have parameter x and y. Type this program and save it as summation.py

#!/usr/bin/env python3

def f(x,y):
return x*y

print(f(3,4))

In this example we have two functions: f(x,y) and print(). The function f(x,y) passed its output to the print function using the return keyword.

function example

Return variables

Functions can return variables. Sometimes a function makes a calculation or has some output, this can be given to the program with a return varaible.

In many cases that output is stored in a variable:

result = f(3,4)
print(result)

In this case the program will call the function f with parameters 3 and 4, then save the output to the variable result.

Exercise

Try the exercises below

1. Make a function that sums the list mylist = [1,2,3,4,5]
2. Can functions be called inside a function?
3. Can a function call itself? (hint: recursion)
4. Can variables defined in a function be used in another function? (hint: scope)

After completing these continue with the next exercise.

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