RNN with them to compute the loss directly. A Tensor can be
     retrieved from a "PackedSequence" object by accessing its ".data"
     attribute.
Parameters:
      * input (Tensor) -- padded batch of variable length
        sequences.
  * **lengths** (*Tensor** or **list**(**int**)*) -- list of
    sequence lengths of each batch element (must be on the CPU if
    provided as a tensor).

  * **batch_first** (*bool**, **optional*) -- if "True", the input
    is expected in "B x T x *" format.

  * **enforce_sorted** (*bool**, **optional*) -- if "True", the
    input is expected to contain sequences sorted by length in a
    decreasing order. If "False", the input will get sorted
    unconditionally. Default: "True".

Returns:
      a "PackedSequence" object
Return type:
      PackedSequence