def __init__(
      self, name, full_name, index, containing_type, fields, options=None,
      serialized_options=None, create_key=None):
    """Arguments are as described in the attribute description above."""
    if create_key is not _internal_create_key:
      _Deprecated('OneofDescriptor')

    super(OneofDescriptor, self).__init__(
        options, serialized_options, 'OneofOptions')
    self.name = name
    self.full_name = full_name
    self.index = index
    self.containing_type = containing_type
    self.fields = fields
Arguments are as described in the attribute description above.
deps/protobuf/python/google/protobuf/descriptor.py