Initializer for _operations.

    Raises:
      TypeError: _graph is not a tf.Graph or mtf.Graph.

    Returns:
      a list of (tf.Operation or mtf.Operation)

def _initialize_operations(self):
    """Initializer for _operations.

    Raises:
      TypeError: _graph is not a tf.Graph or mtf.Graph.

    Returns:
      a list of (tf.Operation or mtf.Operation)
    """
    if isinstance(self._graph, tf.Graph):
      return self._graph.get_operations()
    elif isinstance(self._graph, mtf.Graph):
      return self._graph.operations
    else:
      raise TypeError('Graph is not tf.Graph or mtf.Graph: {}'
                      .format(type(self._graph)))