docs: def logger(self):
          """:class:`logging.Logger` of this instance"""
          if not self.is_main:
              return self.main.logger
          try:
              return self._logger
          except AttributeError:
              name = '%s.%s.%s' % (self.__module__, self.__class__.__name__,
                                   self.num)
              self._logger = logging.getLogger(name)
              self.logger.debug('Initializing...')
              return self._logger