class Adder(object): def __init__(self, starting_sum=0.0): self._current_sum = starting_sum @property def current_sum(self): return self._current_sum def __call__(self, value): self._current_sum += value functor = Adder(starting_sum=42) print("After init", functor.current_sum) functor(1) print("After first call", functor.current_sum) functor(3) print("After second call", functor.current_sum)