Functions in Python can be nested inside other functions.
A function defined inside a function is visible only inside that function.
This is useful to create utilities that are useful to a function, but not useful outside of it.
You might ask: why should I be “hiding” this function, if it does not harm?
One, because it’s always best to hide functionality that’s local to a function, and not useful elsewhere.
Also, because we can make use of closures (more on this later).
Here is an example:
def talk(phrase): def say(word): print(word) words = phrase.split(' ') for word in words: say(word) talk('I am going to buy the milk')
If you want to access a variable defined in the outer function from the inner function, you first need to declare it as
def count(): count = 0 def increment(): nonlocal count count = count + 1 print(count) increment() count()
This is useful especially with closures, as we’ll see later.