code: def sequences_get_mask(sequences, pad_val=0):
      
      mask = np.ones_like(sequences)
      for i, seq in enumerate(sequences):
          for i_w in reversed(range(len(seq))):
              if seq[i_w] == pad_val:
                  mask[i, i_w] = 0
              else:
                  break  # <-- exit the for loop, prepcess next sequence
      return mask
docs: Return mask for sequences.
  
      Parameters
      -----------
      sequences : list of list of int
          All sequences where each row is a sequence.
      pad_val : int
          The pad value.
  
      Returns
      ----------
      list of list of int
          The mask.
  
      Examples
      ---------
      >>> sentences_ids = [[4, 0, 5, 3, 0, 0],
      ...                  [5, 3, 9, 4, 9, 0]]
      >>> mask = sequences_get_mask(sentences_ids, pad_val=0)
      [[1 1 1 1 0 0]
       [1 1 1 1 1 0]]