Closures

A closure happens when an inner function captures variables from the scope where it was defined, even after that scope has finished executing.

def multiplicador(fator):
    def multiplica(n):
        return n * fator   # 'fator' is captured by the closure
    return multiplica

dobro = multiplicador(2)
dobro(10)  # -> 20

They are the foundation of mechanisms like decorators.