Return a list of the (name, value) pairs of the enum.

    These are returned in the order they were defined in the .proto file.

def items(self):
    """Return a list of the (name, value) pairs of the enum.

    These are returned in the order they were defined in the .proto file.
    """
    return [(value_descriptor.name, value_descriptor.number)
            for value_descriptor in self._enum_type.values]