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)