What is nonlocal in Python?

In Python, the keyword nonlocal is used inside nested functions to indicate that a variable refers to the nearest enclosing scope, but not the global scope. This allows modifying a variable from an outer function within an inner function.

Example:

def outer():
    x = 5
    def inner():
        nonlocal x
        x = 10
    inner()
    return x

print(outer())  # Outputs 10

Without nonlocal, attempting to assign a value to x inside inner would create a new local variable, not changing x from outer.