python 自定義回調函數

回調函數用起來比較爽。特別是在js中，滿世界全是回調，那麼在python中，怎麼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.text

a = Anjuke
print a.on_start

在這裡實現的是當self.crawl指定callback方法時，self.crawl會在接收到start_url參數執行完成後回調self.index_url。

而實現方式其實就是通過kwargs獲取到callback的對象/字元串，然後通過getattr(self, callback)來反射得到回調的方法，然後調用即可。

接著可以進一步抽象，增加回調方法的復用，於是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 wrapper

class BaseHandler(object):
　　"""在self.crawl(url,callback=$func)時,通過裝飾器callback即可實現回調,在self.crawl方法中,只需要專註於得到$func的參數即可"""
@callback
def crawl(self, url, **kwargs):
url = quote_chinese(_build_url(url.strip, kwargs.get("params")))
return requests.get(url)

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