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.
You typically don't need to do anything special for the above to work:
>>> def v(f):
... print "decorator v, wrapping", f.__name__, "into a"
... def a(*args, **kw):
... print "calling", f.__name__, "from a"
... return f(*args, **kw)
... return a
...
>>> def w(f):
... print "decorator w, wrapping", f.__name__, "into b"
... def b(*args, **kw):
... print "calling", f.__name__, "from b"
... return f(*args, **kw)
... return b
...
>>> @v
... @w
... def f(s):
... print s
...
decorator w, wrapping f into b
decorator v, wrapping b into a
>>> f("hello")
calling b from a
calling f from b
hello
The output shows that w wraps f into b, but v then doesn't get to see the
original f, it wraps b into a. Put another way
@v
@w
def f(): ...
is the same as
def f(): ...
f = v(w(f))
and calling f() now is equivalent to calling a() which may or may not invoke
b() which may or may not invoke the original f().
Translated into your example:
def post(self, facility_type_id = None): ...
post = auth.login_required(cache.clear(post))
The cache should only be cleared after a successful login, and the original
post() will only be invoked after a successful login and with a cleared
cache.
--
http://mail.python.org/mailman/listinfo/python-list
