docs: def _array_or_placeholder(
      maybe_iterable, placeholder=PLACEHOLDER_ZEROS
  ) -> np.array:
      """
      Return maybe_iterable's contents or a placeholder array.
  
      Used to give bqplot its required initial points to plot even if we're using
      a function to generate points.
      """
      if isinstance(maybe_iterable, collections.Iterable):
          return np.array([i for i in maybe_iterable])
      return placeholder