回调函数用起来比较爽。特别是在js中,满世界全是回调,那么在python中,怎么来优雅地实现自己的回调函数呢
下面贴一个我写的例子
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.text a = Anjuke() print a.on_start()
其实就是通过kwargs获取到callback的对象/字符串,然后通过getattr(self,callback)来反射得到回调的方法,然后调用即可。
接着可以进一步抽象,增加回调方法的复用,于是BaseHandler可以改写成装饰器方式
def callback(f): def wrapper(obj,*args,**kwargs): resp = f(obj,**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 wrapper class BaseHandler(object): @callback def crawl(self,**kwargs): url = quote_chinese(_build_url(url.strip(),kwargs.get('params'))) return requests.get(url)