code: def _zip_flatten(x, ys):
      '''
      intersperse x into ys, with an extra element at the beginning.
      '''
      return itertools.chain.from_iterable(
              zip(itertools.repeat(x), ys)f _zip_flatten(x, ys):
      '''
      intersperse x into ys, with an extra element at the beginning.
      '''
      return itertools.chain.from_iterable(
              zip(itertools.repeat(x), ys))
docs: intersperse x into ys, with an extra element at the beginning.