Configure the loop given the settings.

def config(self, steps_per_epoch, starting_epoch, max_epoch):
        """
        Configure the loop given the settings.
        """
        self.starting_epoch = int(starting_epoch)
        self.max_epoch = int(max_epoch)
        self.steps_per_epoch = int(steps_per_epoch)
        # Allow empty epoch (no steps), if we want to run the callbacks only.
        assert self.steps_per_epoch >= 0 and self.max_epoch >= 0

        self._epoch_num = starting_epoch - 1