'Assert that correct number of anchors was generated.
Args:
anchors: box_list.BoxList object holding anchors generated
feature_map_shape_list: list of (height, width) pairs in the format
[(height_0, width_0), (height_1, width_1), ...] that the generated
anchors must align with.
Returns:
Op that raises InvalidArgumentError if the number of anchors does not
match the number of expected anchors.'

def _assert_correct_number_of_anchors(self, anchors, feature_map_shape_list):

    expected_num_anchors = 0
    for (num_anchors_per_location, feature_map_shape) in zip(self.num_anchors_per_location(), feature_map_shape_list):
        expected_num_anchors += ((num_anchors_per_location * feature_map_shape[0]) * feature_map_shape[1])
    return tf.assert_equal(expected_num_anchors, anchors.num_boxes())
