def _MapItems(message, field):
    """Yields the (key, value) pair of the map values."""
    assert _IsMap(message, field)
    map_message = message.get_assigned_value(field.name)
    additional_properties = map_message.get_assigned_value(
        'additionalProperties')
    for kv_pair in additional_properties:
        yield kv_pair.key, kv_pair.value
Yields the (key, value) pair of the map values.