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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def subscribed(self, build_root, handlers):
 """Bulk subscribe generator for StreamableWatchmanClient. :param str build_root: the build_root for all subscriptions. :param iterable handlers: a sequence of Watchman.EventHandler namedtuple objects. :yields: a stream of tuples in the form (subscription_name: str, subscription_event: dict). """

    command_list = [['subscribe',
                     build_root,
                     handler.name,
                     handler.metadata] for handler in handlers]

    self._logger.debug('watchman command_list is: {}'.format(command_list))

    try:
      for event in self.client.stream_query(command_list):
        if event is None:
          yield None, None
        elif 'subscribe' in event:
          self._logger.info('confirmed watchman subscription: {}'.format(event))
          yield None, None
        elif 'subscription' in event:
          yield event.get('subscription'), event
        else:
          self._logger.warning('encountered non-subscription event: {}'.format(event))
    except self.client.WatchmanError as e:
      raise self.WatchmanCrash(e)