code: def init_progress_bar(self):
          
          # Forked worker processes can't show progress bars.
          disable = MapReduce._forked or not config.PROGRESS_BARS
  
          # Don't materialize iterable unless we have to: huge iterables
          # (e.g. of `KCuts`) eat memory.
          if disable:
              total = None
          else:
              self.iterable = list(self.iterable)
              total = len(self.iterable)
  
          return tqdm(total=total, disable=disable, leave=False,
                      desc=self.description)
docs: Initialize and return a progress bar.