torch.nn.utils.rnn.pack_sequence(sequences: List[Tensor], enforce_sorted: bool = True) → PackedSequence[source]

Packs a list of variable length Tensors

sequences should be a list of Tensors of size L x *, where L is the length of a sequence and * is any number of trailing dimensions, including zero.

For unsorted sequences, use enforce_sorted = False. If enforce_sorted is True, the sequences should be sorted in the order of decreasing length. enforce_sorted = True is only necessary for ONNX export.


>>> from torch.nn.utils.rnn import pack_sequence
>>> a = torch.tensor([1,2,3])
>>> b = torch.tensor([4,5])
>>> c = torch.tensor([6])
>>> pack_sequence([a, b, c])
PackedSequence(data=tensor([ 1,  4,  6,  2,  5,  3]), batch_sizes=tensor([ 3,  2,  1]))
  • sequences (list[Tensor]) – A list of sequences of decreasing length.

  • enforce_sorted (bool, optional) – if True, checks that the input contains sequences sorted by length in a decreasing order. If False, this condition is not checked. Default: True.


a PackedSequence object


Access comprehensive developer documentation for PyTorch

View Docs


Get in-depth tutorials for beginners and advanced developers

View Tutorials


Find development resources and get your questions answered

View Resources