def __len__(self):
        """Return an approximate count of stored state transitions."""
        # TODO: Properly account for indices which can't be used, as in
        # random_batch's check.
        return max(0, self.size - self.phi_length)
dataset/ETHPy150Open spragunr/deep_q_rl/deep_q_rl/ale_data_set.py/DataSet.__len__/original