code: def block(self, callback=None):
          
          self._blocked[callback] = self._blocked.get(callback, 0) + 1
docs: Block this emitter. Any attempts to emit an event while blocked
          will be silently ignored. If *callback* is given, then the emitter
          is only blocked for that specific callback.
  
          Calls to block are cumulative; the emitter must be unblocked the same
          number of times as it is blocked.