code: def run(self):
          
          if self.name and self.name not in self.__class__._has_run:
              self.__class__._has_run.add(self.name)
              ret = self.run_once()
              if ret is not None:
                  yield ret
docs: Make run a no-op if run() has been called before.
  
          Store in a global registry the list of checks we've run. If we have
          run that one before, just skip doing anything the subsequent times.
          This way, since pycodestyle is file/line based, we don't wind
          up re-running a check on a git commit message over and over again.