Python Closures

We've previously seen how to create a nested function in Python.

If you return a nested function from a function, that nested function has access to the variables defined in that function, even if that function is not active any more.

Here is a simple counter example.

def counter():
    count = 0

    def increment():
        nonlocal count
        count = count + 1
        return count

    return increment

increment = counter()

print(increment()) # 1
print(increment()) # 2
print(increment()) # 3

We return the increment() inner function, and that has still access to the state of the count variable even though the counter() function has ended.