回調函數用起來比較爽。特別是在js中，滿世界全是回調，那么在python中，怎么來優雅地實現自己的回調函數呢
下面貼一個我寫的例子
class BaseHandler(object): def crawl(self, url, **kwargs): if kwargs.get('callback'): callback = kwargs['callback'] if isinstance(callback, basestring) and hasattr(self, callback): func = getattr(self, callback) elif hasattr(callback, 'im_self') and callback.im_self is self: func = callback resp = requests.get(url) return func(resp)class Anjuke(BaseHandler): def on_start(self): self.crawl(start_url, callback=self.index_url) def index_url(self, response): print response.texta = Anjuke()print a.on_start()其實就是通過kwargs獲取到callback的對象/字符串，然后通過getattr(self, callback)來反射得到回調的方法，然后調用即可。
接著可以進一步抽象，增加回調方法的復用，于是BaseHandler可以改寫成裝飾器方式
def callback(f): def wrapper(obj, *args, **kwargs): resp = f(obj, *args, **kwargs) if kwargs.get('callback'): mcallback = kwargs['callback'] if isinstance(callback, basestring) and hasattr(obj, mcallback): func = getattr(obj, mcallback) elif hasattr(mcallback, 'im_self') and mcallback.im_self is obj: func = mcallback kwargs['callback'] = func.__name__ else: raise NotImplementedError("self.%s() not implemented!" % callback) return func(resp) return wrapperclass BaseHandler(object): @callback def crawl(self, url, **kwargs): url = quote_chinese(_build_url(url.strip(), kwargs.get('params'))) return requests.get(url)新聞熱點
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