Re: is it possible to see if a class has a decorator ?
On 06-12-2010 16:04, Jean-Michel Pichavant wrote: > Stef Mientki wrote: >> On 06-12-2010 12:08, Ben Finney wrote: >>> Stef Mientki writes: >>> >>> I would like to know if a class definition has a decorator, >>> I'm not sure what this question means. >>> >>> Applying a decorator to a class definition produces a normal class. >>> >>> Classes don't “have” decorators; classes can be returned by a decorator >>> function, but AFAIK the resulting class doesn't “have” the decorator in >>> any sense. >>> >>> is that possible ? >>> The return value of a decorator isn't special in any way, AFAIK. >>> >>> Any function can return a class object or a function object, and any >>> function can be used as a decorator. >>> >>> The only thing that makes a function a decorator is how it is used in >>> the code; but it doesn't leave a trace that I know of. >>> >>> Now, what is it you're trying to do? Perhaps there's a better solution >>> we can come up with. >>> >>> >> Thanks Ben, >> here some more explanation. >> >> I've a number of (dynamic) applications, >> launched from a central wrapper. >> All these modules have a class "Start", which launches the application and >> embeds them in the >> wrapper application. >> >> Module 1: >> class Start (): >> >> >> Module 2: >> @auth >> class Start (): >> ... >> >> When the wrapper application is started, it looks for all dynamic modules >> (without importing them), >> and list these application in a hierarchical tree. >> In the above axmple, >> I would like to know that the class "Start" in Module 2 has the decorator >> "Auth", *without >> importing the module*, >> (so depending on the user logged in, I can decide to add or not add the >> module to the >> hierarchical tree). >> >> thanks, >> Stef Mientki >> >> >> >> > You best bet is to parse the source file. thanks, I was afraid of that. cheers, Stef > > JM -- http://mail.python.org/mailman/listinfo/python-list
Re: is it possible to see if a class has a decorator ?
Stef Mientki wrote: On 06-12-2010 12:08, Ben Finney wrote: Stef Mientki writes: I would like to know if a class definition has a decorator, I'm not sure what this question means. Applying a decorator to a class definition produces a normal class. Classes don't “have” decorators; classes can be returned by a decorator function, but AFAIK the resulting class doesn't “have” the decorator in any sense. is that possible ? The return value of a decorator isn't special in any way, AFAIK. Any function can return a class object or a function object, and any function can be used as a decorator. The only thing that makes a function a decorator is how it is used in the code; but it doesn't leave a trace that I know of. Now, what is it you're trying to do? Perhaps there's a better solution we can come up with. Thanks Ben, here some more explanation. I've a number of (dynamic) applications, launched from a central wrapper. All these modules have a class "Start", which launches the application and embeds them in the wrapper application. Module 1: class Start (): Module 2: @auth class Start (): ... When the wrapper application is started, it looks for all dynamic modules (without importing them), and list these application in a hierarchical tree. In the above axmple, I would like to know that the class "Start" in Module 2 has the decorator "Auth", *without importing the module*, (so depending on the user logged in, I can decide to add or not add the module to the hierarchical tree). thanks, Stef Mientki You best bet is to parse the source file. JM -- http://mail.python.org/mailman/listinfo/python-list
Re: is it possible to see if a class has a decorator ?
On Mon, 06 Dec 2010 22:08:33 +1100, Ben Finney wrote:
> Stef Mientki writes:
>
>> I would like to know if a class definition has a decorator,
>
> I'm not sure what this question means.
>
> Applying a decorator to a class definition produces a normal class.
>
> Classes don't “have” decorators; classes can be returned by a decorator
> function, but AFAIK the resulting class doesn't “have” the decorator in
> any sense.
It seems to me that a class decorator is (usually) like a class factory,
in that it returns a class; the difference being that it takes a pre-
existing class as argument, and (probably) modifies it in place, rather
than creates a new class from scratch.
I say "usually" and "probably" because, of course, a class decorator can
do *anything*. Even something pointless:
>>> def decorator(cls):
... return 1
...
>>> @decorator
... class K:
... pass
...
>>> K
1
>> is that possible ?
>
> The return value of a decorator isn't special in any way, AFAIK.
>
> Any function can return a class object or a function object, and any
> function can be used as a decorator.
[pedant]
Any callable can be a decorator, provided it has an appropriate calling
signature. But you knew that :)
[/pedant]
> The only thing that makes a function a decorator is how it is used in
> the code; but it doesn't leave a trace that I know of.
Function decorators can, because they usually wrap the input function in
a closure, which is detectable:
>>> def decorator(func):
... def inner():
... return func("spam")
... return inner
...
>>>
>>> @decorator
... def ham(s):
... return s.upper()
...
>>> ham.__closure__
(,)
>>>
>>> def cheese(s): # no decorator
... return s.upper()
...
>>> cheese.__closure__
>>>
But this is only a common practice, not a guarantee, because the
decorating function can do anything.
I think that the only way to find out what was used to decorate a class,
or a function, is for the decorator itself to leave some sort of mark on
the wrapped class/function. Perhaps by adding itself to the wrapped
object as an attribute:
def decorate(cls):
cls._decorated_by = decorate
--
Steven
--
http://mail.python.org/mailman/listinfo/python-list
Re: is it possible to see if a class has a decorator ?
On 06-12-2010 12:08, Ben Finney wrote: > Stef Mientki writes: > >> I would like to know if a class definition has a decorator, > I'm not sure what this question means. > > Applying a decorator to a class definition produces a normal class. > > Classes don't “have” decorators; classes can be returned by a decorator > function, but AFAIK the resulting class doesn't “have” the decorator in > any sense. > >> is that possible ? > The return value of a decorator isn't special in any way, AFAIK. > > Any function can return a class object or a function object, and any > function can be used as a decorator. > > The only thing that makes a function a decorator is how it is used in > the code; but it doesn't leave a trace that I know of. > > Now, what is it you're trying to do? Perhaps there's a better solution > we can come up with. > Thanks Ben, here some more explanation. I've a number of (dynamic) applications, launched from a central wrapper. All these modules have a class "Start", which launches the application and embeds them in the wrapper application. Module 1: class Start (): Module 2: @auth class Start (): ... When the wrapper application is started, it looks for all dynamic modules (without importing them), and list these application in a hierarchical tree. In the above axmple, I would like to know that the class "Start" in Module 2 has the decorator "Auth", *without importing the module*, (so depending on the user logged in, I can decide to add or not add the module to the hierarchical tree). thanks, Stef Mientki -- http://mail.python.org/mailman/listinfo/python-list
Re: is it possible to see if a class has a decorator ?
Stef Mientki writes: > I would like to know if a class definition has a decorator, I'm not sure what this question means. Applying a decorator to a class definition produces a normal class. Classes don't “have” decorators; classes can be returned by a decorator function, but AFAIK the resulting class doesn't “have” the decorator in any sense. > is that possible ? The return value of a decorator isn't special in any way, AFAIK. Any function can return a class object or a function object, and any function can be used as a decorator. The only thing that makes a function a decorator is how it is used in the code; but it doesn't leave a trace that I know of. Now, what is it you're trying to do? Perhaps there's a better solution we can come up with. -- \ “Pinky, are you pondering what I'm pondering?” “I think so, | `\ Brain, but there's still a bug stuck in here from last time.” | _o__) —_Pinky and The Brain_ | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
is it possible to see if a class has a decorator ?
hello, I would like to know if a class definition has a decorator, is that possible ? And if so, is it possible to determine the name of these decorator(s) ? thanks, Stef Mientki -- http://mail.python.org/mailman/listinfo/python-list
