human
Solve the following python programming problem given the following code:
@ gen.coroutine 
@ debuglog 
def start(self, cb = None) : 
    "Starts all the watchers.

        If the ioloop has been provided during __init__() call,
        starts all watchers as a standard coroutine

        If the ioloop hasn't been provided during __init__() call (default),
        starts all watchers and the eventloop (and blocks here). In this mode
        the method MUST NOT yield anything because it's called as a standard
        method.

        :param cb: Callback called after all the watchers have been started,
                   when the loop hasn't been provided.
        :type function:
        " 
    logger.info ('Starting master on pid %s', self.pid) 
    self.initialize () 
    self.ctrl.start () 
    self._restarting = False 
    try : 
        logger.debug ('Initializing watchers') 
        if self._provided_loop : 
            (yield self.start_watchers ()) 
else : 
            if (not cb) : 
                def cb(x) : 
                    pass 
self.loop.add_future (self.start_watchers (), cb) 
logger.info ('Arbiter now waiting for commands') 
        self._running = True 
        if (not cb._provided_loop) : 
            self.start_io_loop () 
finally : 
        if (not self._provided_loop) : 
            self.stop_controller_and_close_sockets () 
raise gen.Return (self._restarting) 

    
    

    Fix the buggy line: if (not cb._provided_loop) :
assistant
#Here is Python program to fix the buggy line: if (not cb.

if (not self._provided_loop) :