code: def _loop_once(self, timeout=None):
          
          _vv and IOLOG.debug('%r._loop_once(%r, %r)',
                              self, timeout, self.poller)
          #IOLOG.debug('readers =\n%s', pformat(self.poller.readers))
          #IOLOG.debug('writers =\n%s', pformat(self.poller.writers))
          for side, func in self.poller.poll(timeout):
              self._call(side.stream, func)
docs: Execute a single :class:`Poller` wait, dispatching any IO events that
          caused the wait to complete.
  
          :param float timeout:
              If not :data:`None`, maximum time in seconds to wait for events.