@tornado.gen.engine and @tornado.web.asynchronous

[Nick Baum]

The docs specify that I need to include both @tornado.gen.engine and @tornado.web.asynchronous for async handlers that use gen.

However, my code seems to work just fine with just the @tornado.gen.engine decorator. There are no duplicate calls to self.finish, and I don't have to call finish manually.

Am I missing something? Are there edge cases where it will break?

-Nick

[aliane abdelouahab]

about self.finish():
it is called when you do self.render() or self.redirect()
but if you just make something that dont use those two, you will have
a browser turning untill giving an error like the server dont work,
this is where you must call self.finish() explicitly.

[aliane abdelouahab]

as an example where you must use self.finish():
self.write() this one if you use it, your browser will hang! you must
call explicitly self.finish() after self.write()
for the first question, hope someone else can help, i think i saw the
answer but dont remember where.

On 11 avr, 23:47, Nick Baum <nickb...@whereberry.com> wrote:

[aliane abdelouahab]

got it, here is the thread:
https://groups.google.com/group/python-tornado/browse_thread/thread/aa9dab35144457d1/0dba6c1c3e2712a3?hl=fr&lnk=gst&q=%40engine+and+%40asynchronous#0dba6c1c3e2712a3

[Ben Darnell]

Aliane is right; if a handler method uses @gen.engine you need to also use @asynchronous (at least as long as the generator yields anything interesting).  @gen.coroutine is a little more magic:  as of 3.0.1 if you use both @asynchronous and @gen.coroutine you don't have to call finish() explicitly (this isn't documented because it was a side effect of the 3.0.1 patch and wasn't in 3.0). In 3.1 I think you'll be able to use @gen.coroutine without @asynchronous, as well as use @gen.coroutine on methods that cannot currently be made asynchronous like prepare().

-Ben 

On Thu, Apr 11, 2013 at 8:27 PM, aliane abdelouahab <alabde...@gmail.com> wrote:

got it, here is  the thread:
https://groups.google.com/group/python-tornado/browse_thread/thread/aa9dab35144457d1/0dba6c1c3e2712a3?hl=fr&lnk=gst&q=%40engine+and+%40asynchronous#0dba6c1c3e2712a3

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[aliane abdelouahab]

thank you for the explications :)

On 12 avr, 01:59, Ben Darnell <b...@bendarnell.com> wrote:
> Aliane is right; if a handler method uses @gen.engine you need to also use
> @asynchronous (at least as long as the generator yields anything
> interesting).  @gen.coroutine is a little more magic:  as of 3.0.1 if you
> use both @asynchronous and @gen.coroutine you don't have to call finish()
> explicitly (this isn't documented because it was a side effect of the 3.0.1
> patch and wasn't in 3.0). In 3.1 I think you'll be able to use
> @gen.coroutine without @asynchronous, as well as use @gen.coroutine on
> methods that cannot currently be made asynchronous like prepare().
>
> -Ben
>

> On Thu, Apr 11, 2013 at 8:27 PM, aliane abdelouahab <alabdeloua...@gmail.com

>
>
>
>
>
>
>
> > wrote:
> > got it, here is  the thread:
>

> >https://groups.google.com/group/python-tornado/browse_thread/thread/a...

[Nick Baum (StoryWorth)]

Thanks Aliane and Ben, I'm still not sure I understand though.

Let's say my handler looks like this:

@tornado.gen.engine

def post(self)

    url = yield tornado.gen.Task(self.process_post)

    self.redirect(url)

def process_post(self, callback)

    ...

    callback(url)

Do I need to decorate the post method with @tornado.web.asynchronous, and if so, why?

-Nick

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Nick Baum

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650-704-1546

[aliane abdelouahab]

when you call a decorator, here is what you do:
http://stackoverflow.com/questions/739654/understanding-python-decorators/1594484#1594484
so you are modifying this:
https://github.com/facebook/tornado/blob/master/tornado/web.py#L1149

On 12 avr, 02:16, "Nick Baum (StoryWorth)" <n...@storyworth.com>
wrote:

> Thanks Aliane and Ben, I'm still not sure I understand though.
>
> Let's say my handler looks like this:
>
> @tornado.gen.engine
> def post(self)
>     url = yield tornado.gen.Task(self.process_post)
>     self.redirect(url)
>
> def process_post(self, callback)
>     ...
>     callback(url)
>
> Do I need to decorate the post method with @tornado.web.asynchronous, and
> if so, why?
>
> -Nick
>

> On Thu, Apr 11, 2013 at 6:10 PM, aliane abdelouahab <alabdeloua...@gmail.com

> >https://groups.google.com/d/topic/python-tornado/7ELZz6H7TK8/unsubscr...
> > .

> > To unsubscribe from this group and all its topics, send an email to
> > python-tornad...@googlegroups.com.

> > For more options, visithttps://groups.google.com/groups/opt_out.

[Ben Darnell]

On Thu, Apr 11, 2013 at 9:16 PM, Nick Baum (StoryWorth) <ni...@storyworth.com> wrote:

Thanks Aliane and Ben, I'm still not sure I understand though.

Let's say my handler looks like this:

@tornado.gen.engine

def post(self)

    url = yield tornado.gen.Task(self.process_post)

    self.redirect(url)

def process_post(self, callback)

    ...

    callback(url)

Do I need to decorate the post method with @tornado.web.asynchronous, and if so, why?

Depends on what process_post does.  If it runs straight through and runs the callback immediately, then you may not need @asynchronous (and in that case you're not gaining anything by making it take a callback and calling it with gen.Task).  If it runs the callback asynchronously (e.g. if process_post also has @gen.engine and yields something), then you definitely need @asynchronous on post().  Without @asynchronous, the post may return an empty 200 to the client before reaching the redirect.

-Ben

[Nick Baum (StoryWorth)]

Ah, I get it. The reason my handlers worked without the @asynchronous decorator is that the only ones that were doing asynchronous work didn't actually need to return any content to the browser (they could essentially call finish right away).

So in fact it was an edge case that it actually worked!

Thanks for the explanations.

-Nick