code: def stack(xs, dim_name, axis=0, name=None):
    
    ret = StackOperation(xs, dim_name, axis, name).outputs[0]
    return ret
docs: Stack multiple Tensors to make a new dimension.
  
    Args:
      xs: a list of Tensors with identical shapes.
      dim_name: a string (name of the new dimension)
      axis: an integer (index of the new dimension in the output shape)
      name: an optional string
  
    Returns:
      a Tensor