The Python Apprentice

Defining functions

Functions are defined using the def keyword followed by the function name, an argument list in parentheses, and a colon to start a new block. Let's quickly define a few functions at the REPL to get the idea:

>>> def square(x):...     return x * x...

We use the return keyword to return a value from the function.

As we've seen previously, we call functions by providing the actual arguments in parentheses after the function name:

>>> square(5)5

Functions aren't required to explicitly return a value though — perhaps they produce side effects:

>>> def launch_missiles():...     print("Missiles launched!")...>>> launch_missiles()Missiles launched!

You can return early from a function by using the return keyword with no parameter:

>>> ...