code: def sg_expand_dims(tensor, opt):
      r
      opt += tf.sg_opt(axis=-1)
      return tf.expand_dims(tensor, opt.axis, name=opt.name)
docs: r"""Inserts a new axis.
      
      See tf.expand_dims() in tensorflow.
  
      Args:
        tensor: A `Tensor` (automatically given by chain).
        opt:
          axis : Dimension to expand. Default is -1.
          name: If provided, it replaces current tensor's name.
  
      Returns:
          A `Tensor`.