human
Solve the following python programming problem given the following code:
def apply(self, fgraph, start_from = None) : 
    if (start_from is None) : 
        start_from = fgraph.outputs 
callback_before = fgraph.execute_callbacks_time 
    nb_nodes_start = len (fgraph.apply_nodes) 
    t0 = time.time () 
    q = deque (graph.io_toposort (fgraph.inputs, start_from)) 
    io_t = (time.time () - t0) 
    def importer(node) : 
        if (node is not current_node) : 
            q.append (node) 
def pruner(node) : 
        if (node is not current_node) : 
            try : 
                q.remove (node) 
except ValueError : 
                pass 
u = self.attach_updater (fgraph, importer, pruner) 
    nb = 0 
    try : 
        t0 = time.time () 
        while q : 
            if (self.order == 'out_to_in') : 
                node = q.pop () 
else : 
                node = q.popleft () 
current_node = node 
            nb += self.process_node (fgraph, node) 
loop_t = (time.time () - callback_before) 
except Exception : 
        self.detach_updater (fgraph, u) 
        raise 
self.detach_updater (fgraph, u) 
    callback_time = (fgraph.execute_callbacks_time - callback_before) 
    nb_nodes_end = len (fgraph.apply_nodes) 
    return (self, nb, nb_nodes_start, nb_nodes_end, io_t, loop_t, callback_time) 

    
    

    Fix the buggy line: loop_t = (time.time () - callback_before)
assistant
#Here is Python code to fix the buggy line: loop_t = (time.

loop_t = (time.time () - t0)