human
Solve the following python programming problem given the following code:
def __init__(self, runs, conn, robot, reactor) : 
    self._conn = conn 
    self._robot = robot 
    self._tests = [RemoteTest (conn, self.TAG, name) for name in self.TYPES] 
    self._deferred = d = Deferred () 
    d.addCallback (self._setup) 
    d.addCallback (delay, 20, reactor) 
    for _ in xrange (runs) : 
        for test in self._tests : 
            d.addCallback (test.run) 
d.addCallback (reactor._postProcess) 
    d.addCallback (delay, 2, reactor) 
    def stop(_) : 
        reactor.stop () 
        print ('
done') 
d.addCallback (stop) 

    
    

    Fix the buggy line: d.addCallback (reactor._postProcess)
assistant
#Here is Python program to fix the buggy line: d.

d.addCallback (self._postProcess)