code: def for_default_graph(*args, **kwargs):
    
    graph = tf.get_default_graph()
    collection = graph.get_collection(_BOOKKEEPER)
    if collection:
      if args or kwargs:
        raise ValueError('Requesting construction of a BookKeeper that already '
                         'exists: %s %s' % (args, kwargs))
      return collection[0]
    else:
      books = BOOKKEEPER_FACTORY(*args, g=graph, **kwargs)
      graph.add_to_collection(_BOOKKEEPER, books)
      return books
docs: Creates a bookkeeper for the default graph.
  
    Args:
      *args: Arguments to pass into Bookkeeper's constructor.
      **kwargs: Arguments to pass into Bookkeeper's constructor.
    Returns:
      A new Bookkeeper.
    Raises:
      ValueError: If args or kwargs are provided and the Bookkeeper already
        exists.