def add_list(self):
    """Appends and returns a list value as the next value in the list."""
    list_value = self.values.add().list_value
    # Clear will mark list_value modified which will indeed create a list.
    list_value.Clear()
    return list_value
Appends and returns a list value as the next value in the list.
deps/protobuf/python/google/protobuf/internal/well_known_types.py