python 类方法__call__拦截调用实例介绍
python类，如果定义了__call__方法，
定义类型的时候，实现__call__函数，这个类型就成为可调用的。
换句话说，我们可以把这个类型的对象当作函数来使用，相当于 重载了括号运算符。
会为实例应用函数调用表达式运行__call__方法，好处是：
可以让类实例的外观和用法类似于函数。
可编写遵循所需要的函数来调用接口对象，同时又能够保留状态信息。
实例1：
1 class temp: 2 def __init__(self, data): 3 self.data = data 4 def __call__(self, other): 5 return self.data * other 6 7 ins1 = temp(3) 8 print ins1.data 9 3 10 print ins1(5) 11 15 12 13 class temp: 14 def __init__(self, data): 15 self.data = data 16 def __call__(self, other): 17 return self.data(other) * other 18 19 ins2 = temp(lambda x:x+1) 20 ins2.data 21 <function __main__.<lambda>> 22 ins2(3) 23 12
实例2
1 class temp: 2 def __init__(self, arg1, arg2): 3 self.arg1 = arg1 4 self.arg2 = arg2 5 def __call__(self, other): 6 return self.arg1(other)*other, self.arg2(other)*other 7 8 ins = temp(lambda x:x+1, lambda y:y*2) 9 10 print ins.arg1 11 <function __main__.<lambda>> 12 13 print ins.arg2 14 <function __main__.<lambda>> 15 16 17 ins(4) 18 (20, 32)
实例3
memcached存储实例：
mc.get(key) 从memcached中取key对应的value
mc.set(key, value, timeout) 设置key-vlaue对
User是个用户类
Order是一个订单类
1 import mc, User, Order 2 3 class McNum(object): 4 def __init__(self, get_num, mc_key, timeout): 5 self.get_num = get_num 6 self.mc_key = mc_key 7 self.timeout = timeout 8 9 def __call__(self, *key): 10 mkey = self.mc_key % '_'.join(map(str, key)) 11 num = mc.get(mkey) 12 if num in None: 13 num = self.get_num(*key) or 0 14 mc.set(mkey, num, self.timeout) 15 return num 16 17 get_user_name_count_by_state = McNum( 18 lambda state:User.where(state=state).count(), 19 'UserNameCountByState:%s' 20 ) 21 22 get_order_count_by_user_id = McNum( 23 lambda user_id:Order.where(user_id=user_id).count(), 24 'OrderCountByUserId%s' 25 ) 26 27 if __name__ == "__main__": 28 state = [1, 2, 3, 4] 29 user_ids = [12232, 23443, 66433, 23356] 30 for i in state: 31 get_user_name_count_by_state(i) 32 for j in user_ids: 33 get_order_count_by_user_id(j)
实例4
将__call__所要调用的函数至于类外
1 def _get(self, *key): 2 mkey = self.key_pattern % key 3 result = mc.get(mkey) 4 if result in None: 5 return result 6 7 class McNum(object): 8 def __init__(self, key_pattern): 9 self.key_pattern = key_pattern 10 11 __call__ = _get 12 13 get_user_name_count_by_state = McCacheA( 14 'UserNameCountByState:%s' 15 ) 16 17 18 if __name__ == "__main__": 19 state = [1, 2, 3, 4] 20 for i in state: 21 get_user_name_count_by_state(i)
结论
