python构建自定义回调函数详解

Python  /  管理员 发布于 7年前   133

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