def ValidateUnusedShapes(self, problems):
    # Check for unused shapes
    known_shape_ids = set(self._shapes.keys())
    used_shape_ids = set()
    for trip in self.GetTripList():
      used_shape_ids.add(trip.shape_id)
    unused_shape_ids = used_shape_ids - known_shape_ids
    if unused_shape_ids:
      problems.OtherProblem('The shapes with the following shape_ids aren\'t '
                            'used by any trips: %s' %
                            ', '.join(unused_shape_ids),
                            type=problems_module.TYPE_WARNING)
dataset/ETHPy150Open google/transitfeed/transitfeed/schedule.py/Schedule.ValidateUnusedShapes/swapped operands of `-`