python构建自定义回调函数详解

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)

来源：http://www.cnblogs.com/alexkn/p/7051193.html