code: def refresh(self, line=None):
          
          # Just go away if it is locked. Will update next time
          if not self._lock.acquire(False):
              return
  
          if line is None:
              line = self._line
  
          if sys.stdout.isatty() and line is not None:
              self._writeln(line)
              self._line = line
  
          self._lock.release()
docs: Refreshes progress bar.