def begin(self, max_steps=None):
    super(CheckpointSaver, self).begin(max_steps)
    self._last_saved_time = None
    self._last_begin_step = None
    self._last_saved_step = None
def begin(self, max_steps=None):
    super(CheckpointSaver, self).begin(max_steps)
    self._last_saved_time = None
    self._last_begin_step = None
    self._last_saved_step = None