nonlocal in Python 3

#TIL about nonlocal in Python 3

Inner functions can access outer variables but can’t modify them by default

Here’s a contrived simple example

def outer():
    num = 0
    def inner():
        nonlocal num
        num += 1
    inner()

If you remove the nonlocal result, you’ll get an UnboundLocalError

UnboundLocalError: cannot access local variable 'result' where it is not associated with a value

Most of the time, it might be a code smell (given the global variable).

Never encountered it until writing messy Leetcode!