def add_time_step(self, **create_time_step_kwargs):
    """Creates a time-step and appends it to the list.

    Args:
      **create_time_step_kwargs: Forwarded to
        time_step.TimeStep.create_time_step.
    """
    ts = time_step.TimeStep.create_time_step(**create_time_step_kwargs)
    assert isinstance(ts, time_step.TimeStep)
    self._time_steps.append(ts)
Creates a time-step and appends it to the list.

    Args:
      **create_time_step_kwargs: Forwarded to
        time_step.TimeStep.create_time_step.