def __getitem__(self, key):
    try:
      return self._values[key]
    except __HOLE__:
      key = self._key_checker.CheckValue(key)
      new_element = self._message_descriptor._concrete_class()
      new_element._SetListener(self._message_listener)
      self._values[key] = new_element
      self._message_listener.Modified()

      return new_element
dataset/ETHPy150Open sklearn-theano/sklearn-theano/sklearn_theano/externals/google/protobuf/internal/containers.py/MessageMap.__getitem__