1用 python实现个 异步的 http服务（太难）
class cached_property(object):
""" A property that is only computed once per instance and then replaces
itself with an ordinary attribute. Deleting the attribute resets the
property. """
def __init__(self, func):
update_wrapper(self, func)
self.func = func
def __get__(self, obj, cls):
if obj is None: return self
value = obj.__dict__[self.func.__name__] = self.func(obj)
return value
给celery贡献代码