Functions in Python (With Examples)

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.

Python Function Examples

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.

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.

Practice Exercises

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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