:meth:`.WSignalSourceProto.watch` implementation

		:rtype: watcher: WSignalSource.Watcher

def watch(self, signal_name):
		""" :meth:`.WSignalSourceProto.watch` implementation

		:rtype: watcher: WSignalSource.Watcher
		"""
		watcher = WSignalSource.Watcher(
			self.__queues[signal_name], lambda x: self.__watchers_callbacks[signal_name].remove(x)
		)
		self.__watchers_callbacks[signal_name].add(watcher)
		return watcher