code: def _stride(stride_spec):
    
    if stride_spec is None:
      return [1, 1, 1, 1]
    elif isinstance(stride_spec, tf.compat.integral_types):
      return [1, stride_spec, stride_spec, 1]
    elif len(stride_spec) == 1:
      return [1, stride_spec[0], stride_spec[0], 1]
    elif len(stride_spec) == 2:
      return [1, stride_spec[0], stride_spec[1], 1]
    else:
      assert len(stride_spec) == 4
      return stride_spec
docs: Expands the stride spec into a length 4 list.
  
    Args:
      stride_spec: If length 0, 1 or 2 then assign the inner dimensions, otherwise
        return stride_spec if it is length 4.
    Returns:
      A length 4 list.