human
Solve the following python programming problem given the following code:
def add_session_callback(self, callback) : 
    def cleanup(func) : 
        if (callback.id in self._removers) : 
            del self._removers [callback.id] 
if isinstance (callback, PeriodicCallback) : 
        remover = self._group.add_periodic_callback (callback.callback, callback.period, cleanup) 
else : 
        if isinstance (remover, TimeoutCallback) : 
            remover = self._group.add_timeout_callback (callback.callback, callback.timeout, cleanup) 
else : 
            if isinstance (callback, NextTickCallback) : 
                remover = self._group.add_next_tick_callback (callback.callback, cleanup) 
else : 
                raise ValueError (('Expected callback of type PeriodicCallback, TimeoutCallback, NextTickCallback, got: %s' % callback.callback)) 
self._removers [callback.id] = remover 

    
    

    Fix the buggy line: if isinstance (remover, TimeoutCallback) :
assistant
#Here is Python program to fix the buggy line: if isinstance (remover, TimeoutCallback) :
.

if isinstance (callback, TimeoutCallback) :