Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!weretis.net!feeder1.news.weretis.net!feeder.erje.net!newsfeed.xs4all.nl!newsfeed5.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Date: Sat, 06 Aug 2011 09:49:30 +0200
From: =?ISO-8859-1?Q?Rafael_Dur=E1n_Casta=F1eda?= <rafadurancastaneda@gmail.com>
User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.18) Gecko/20110617 Thunderbird/3.1.11
MIME-Version: 1.0
To: python-list@python.org
Subject: Re: How do I implement two decorators in Python both of which would eventually want to call the calling function
References: <8b087624-4e05-4d2e-bf4f-78383202b7e1@28g2000pry.googlegroups.com>
In-Reply-To: <8b087624-4e05-4d2e-bf4f-78383202b7e1@28g2000pry.googlegroups.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.1964.1312616975.1164.python-list@python.org>
Lines: 68
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:10960

You don't need doing something special, each decorator returns a new 
function that and only the result function formed by all decorators will 
be run. Consider this:

def clear_cache(func):
     def decorator(*args, **kwargs):
         print "cache cleared"
         return func(*args, **kwargs)
     return decorator


def login(func):
     def decorator(*args, **kwargs):
         print "login"
         return func(*args, **kwargs)
     return decorator

@login
@clear_cache
def post(msg= "POST", *args):
     print msg
     return args


result = post("POST", "something")
print result

The output will be:

login
cache cleared
POST
('something',)

On 06/08/11 07:49, Devraj wrote:
> Hi all,
>
> I am trying to simply my Web application handlers, by using Python
> decorators.
>
> Essentially I want to use decorators to abstract code that checks for
> authenticated sessions and the other that checks to see if the cache
> provider (Memcache in this instance) has a suitable response.
>
> Consider this method definition with the decorators:
>
> @auth.login_required
> @cache.clear
> def post(self, facility_type_id = None):
>
> auth.login_required checks to see if the user is logged in, otherwise
> returns an appropriate error message, or executes the original
> function.
>
> cache.clear would check to to see if the cache has a particular key
> and drop that, before it executes the calling method.
>
> Both auth.login_required and cache.clear would want to eventually
> execute the calling method (post).
>
> > From what I've read both, doing what I am doing now would execute the
> calling method (post) twice.
>
> My question, how do I chain decorators that end up executing the
> calling method, but ensure that it's only called once.
>
> Appreciate any pointers and thanks for your time.