code: def learning_schedule() -> Callable:
      
  
      def parse(schedule_str):
          try:
              schedule = LearningRateSchedulerFixedStep.parse_schedule_str(schedule_str)
          except ValueError:
              raise argparse.ArgumentTypeError(
                  "Learning rate schedule string should have form rate1:num_updates1[,rate2:num_updates2,...]")
          return schedule
  
      return parse
docs: Returns a method that can be used in argument parsing to check that the argument is a valid learning rate schedule
      string.
  
      :return: A method that can be used as a type in argparse.