code: def random_sequences(length_from, length_to,
                       vocab_lower, vocab_upper,
                       batch_size):
      
      if length_from > length_to:
              raise ValueError('length_from > length_to')
  
      def random_length():
          if length_from == length_to:
              return length_from
          return np.random.randint(length_from, length_to + 1)
      
      while True:
          yield [
              np.random.randint(low=vocab_lower,
                                high=vocab_upper,
                                size=random_length()).tolist()
              for _ in range(batch_size)
          ]
docs: Generates batches of random integer sequences,
          sequence length in [length_from, length_to],
          vocabulary in [vocab_lower, vocab_upper]