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python 自定义回调函数

2017-06-20 00:41 本站整理 浏览(3)

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, *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 wrapper


class BaseHandler(object):

    @callback
    def crawl(self, url, **kwargs):
        url = quote_chinese(_build_url(url.strip(), kwargs.get('params')))
        return requests.get(url)