code: def sg_concat(tensor, opt):
      r
      assert opt.target is not None, 'target is mandatory.'
      opt += tf.sg_opt(axis=tensor.get_shape().ndims-1)
      target = opt.target if isinstance(opt.target, (tuple, list)) else [opt.target]
      return tf.concat([tensor] + target, opt.axis, name=opt.name)
docs: r"""Concatenates tensors along a axis.
  
      See `tf.concat()` in tensorflow.
  
      Args:
        tensor: A `Tensor` (automatically given by chain).
        opt:
          target: A `Tensor`. Must have the same rank as `tensor`, and
            all dimensions except `opt.dim` must be equal.
          axis : Target axis. Default is the last one.
          name: If provided, replace current tensor's name.
  
      Returns:
        A `Tensor`.