Nested list of variable length to a tensor 
  
  
    This code might work: 
target = [[[1,2,3], [2,4,5,6]], [[1,2,3], [2,4,5,6], [2,4,6,7,8]]]
max_cols = max([len(row) for batch in target for row in batch])
max_rows = max([len(batch) for batch in target])
padded = [batch + [[0] * (max_cols)] * (max_rows - len(batch)) for batch in target]
padded = torch.tensor([row + [0] * (max_length - len(row)) for batch in padded for row in batch])
padded = padded.view(-1, max_rows, max_cols)