I am just learning python, and I am currently playing with Tornado framework. I see this class:
class AuthHandler(BaseHandler, tornado.auth.GoogleMixin):
@tornado.web.asynchronous
def get(self):
if self.get_argument("openid.mode", None):
self.get_authenticated_user(self.async_callback(self._on_auth))
return
self.authenticate_redirect()
I am having trouble grasping what the decorator does there (@tornado.web.asynchronous). Does it overwrite that function?
You can see the full source at https://github.com/facebook/tornado/blob/master/demos/chat/chatdemo.py
Yes, it probably does, but it proprably retains a reference to the original get(self) definition.
Python decorators are nothing more than a callable themselves (a function, or a class instance with a __call__ method). Whatever that callable returns is used as the definition for the decorated function instead.
If I define a simple no-op decorator like this, that means that I replace the original with…. the original:
def noopDecorator(func):
return func
The @ symbol used for decorators is syntactic sugar, you could also write it as:
class AuthHandler(BaseHandler, tornado.auth.GoogleMixin):
def get(self):
if self.get_argument("openid.mode", None):
self.get_authenticated_user(self.async_callback(self._on_auth))
return
self.authenticate_redirect()
get = tornado.web.asynchronous(get)
In the case of the tornado asynchronous decorator, the decorator probably returns a deferred handler, to handle the decorated function asynchronously, keeping you, the programmer of a tornado-based application, from having to remember the intricacies of how to do that, time and again. In short, it let’s you focus on the details of your application instead.
1
You can see the documentation for @tornado.web.asynchronous can be found here http://www.tornadoweb.org/documentation/web.html#tornado.web.asynchronous.
But basically it means that the method will be run asynchronously if possible.