code: def add_progress(self, delta, done=None):
          
          if done is not None:
              self.done = done
          self.bar.current = max(min(self.done, self.current + delta), 0)
          self.rate_display.set_text(self.rate_text)
          self.remaining_time_display.set_text(self.remaining_time_text)
          return self.current == self.done
docs: Add to the current progress amount
  
          Add `delta` to the current progress amount. This also updates
          :attr:`rate` and :attr:`remaining_time`.
  
          The :attr:`current` progress is never less than 0 or greater
          than :attr:`done`.
  
          :param delta: amount to add, may be negative
          :param done: new value to use for done