How to pad the left side of a list of tensors in pytorch to the size of the largest list?
In pytorch, if you have a list of tensors, you can pad the right side using torch.nn.utils.rnn.pad_sequence
import torch
'for the collate function, pad the sequences'

f = [
    [0,1],
    [0, 3, 4],
    [4, 3, 2, 4, 3]
]

torch.nn.utils.rnn.pad_sequence(
    [torch.tensor(part) for part in f],
    batch_first=True
)

tensor([[0, 1, 0, 0, 0],
        [0, 3, 4, 0, 0],
        [4, 3, 2, 4, 3]])

How would I pad the left side? The desired solution is
tensor([[0, 0, 0, 0, 1],
        [0, 0, 0, 3, 4],
        [4, 3, 2, 4, 3]])


You can reverse the list, do the padding, and reverse the tensor. Would that be acceptable to you? If yes, you can use the code below.
torch.nn.utils.rnn.pad_sequence([
    torch.tensor(i[::-1]) for i in f 
  ],                                 # reverse the list and create tensors 
  batch_first=True)                  # pad
  .flip(dims=[1])                    # reverse/flip the padded tensor in first dimension

