This is fixed in Python 3 with the nonlocal keyword. In Python 2, the idiomatic work-around is to have x be list of one item: def f(): x = [0]

This is fixed in Python 3 with the nonlocal keyword. In Python 2, the idiomatic work-around is to have x be list of one item: def f(): x = [0] def add(amt): x[0] += amt add(10) return x[0]