class Every:

    def __init__(self, every):
        self._every = every
        self._last = None

    def __call__(self, step):
        step = int(step)
        if not self._every:
            return False
        if self._last is None:
            self._last = step
            return True
        if step >= self._last + self._every:
            self._last += self._every
            return True
        return False


class Once:

    def __init__(self):
        self._once = True

    def __call__(self):
        if self._once:
            self._once = False
            return True
        return False


class Until:

    def __init__(self, until):
        self._until = until

    def __call__(self, step):
        step = int(step)
        if not self._until:
            return True
        return step < self._until