code: def map_(input_layer, fn):
    
    if not input_layer.is_sequence():
      raise ValueError('Can only map a sequence.')
    return [fn(x) for x in input_layer]
docs: Maps the given function across this sequence.
  
    To map an entire template across the sequence, use the `as_fn` method on the
    template.
  
    Args:
      input_layer: The input tensor.
      fn: A function of 1 argument that is applied to each item in the sequence.
    Returns:
      A new sequence Pretty Tensor.
    Raises:
      ValueError: If the input_layer does not hold a sequence.