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Re: Decorators not worth the effort

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Steven D'Aprano於 2012年9月15日星期六UTC+8上午7時39分28秒寫道：
> On Fri, 14 Sep 2012 15:16:47 -0600, Ian Kelly wrote:
> 
> 
> 
> > If only there were a conceptually simpler way to do this.  Actually,
> 
> > there is.  I give you: metadecorators!
> 
> [code snipped but shown below]
> 
> > Which I think is certainly easier to understand than the nested
> 
> > functions approach.
> 
> 
> 
> Maybe for you, but to me it is a big ball of mud. I have no idea how this 
> 
> is supposed to work! At a quick glance, I would have sworn that it 
> 
> *can't* work, since simple_decorator needs to see multiple arguments but 
> 
> only receives one, the function to be decorated. And yet it does work:
> 
> 
> 
> py> from functools import partial
> 
> py> def make_wrapper(wrapper):
> 
> ...     return lambda wrapped: partial(wrapper, wrapped)
> 
> ...
> 
> py> @make_wrapper
> 
> ... def simple_decorator(func, *args, **kwargs):
> 
> ...     print "Entering decorated function"
> 
> ...     result = func(*args, **kwargs)
> 
> ...     print "Exiting decorated function"
> 
> ...     return result
> 
> ...
> 
> py> @simple_decorator
> 
> ... def my_function(a, b, c):
> 
> ...     """Doc string"""
> 
> ...     return a+b+c
> 
> ...
> 
> py> my_function(1, 2, 3)
> 
> Entering decorated function
> 
> Exiting decorated function
> 
> 6
> 
> 
> 
> So to me, this is far more magical than nested functions. If I saw this 
> 
> in t requires me to hunt through your library for the "simple function 
> 
> buried in a utility module somewhere" (your words), instead of seeing 
> 
> everything needed in a single decorator factory function. It requires 
> 
> that I understand how partial works, which in my opinion is quite tricky. 
> 
> (I never remember how it works or which arguments get curried.)
> 
> 
> 
> And the end result is that the decorated function is less debugging-
> 
> friendly than I demand: it is an anonymous partial object instead of a 
> 
> named function, and the doc string is lost. And it is far from clear to 
> 
> me how to modify your recipe to use functools.wraps in order to keep the 
> 
> name and docstring, or even whether I *can* use functools.wraps.
> 
> 
> 
> I dare say I could answer all those questions with some experimentation 
> 
> and research. But I don't think that your "metadecorator" using partial 
> 
> is *inherently* more understandable than the standard decorator approach:
> 
> 
> 
> def simple_decorator2(func):
> 
>     @functools.wraps(func)
> 
>     def inner(*args, **kwargs):
> 
>         print "Entering decorated function"
> 
>         result = func(*args, **kwargs)
> 
>         print "Exiting decorated function"
> 
>         return result
> 
>     return inner
> 
> 
> 
> This is no more complex than yours, and it keeps the function name and 
> 
> docstring.
> 
> 
> 
> 
> 
> > Parameterized decorators are not much more
> 
> > difficult this way.  This function:
> 
> [snip code]
> 
> > And now we have a fancy parameterized decorator that again requires no
> 
> > thinking about nested functions at all.
> 
> 
> 
> Again, at the cost of throwing away the function name and docstring.
> 
> 
> 
> I realise that a lot of this boils down to personal preference, but I 
> 
> just don't think that nested functions are necessarily that hard to 
> 
> grasp, so I prefer to see as much of the decorator logic to be in one 
> 
> place (a nested decorator function) rather than scattered across two 
> 
> separate decorators plus partial.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> -- 
> 
> Steven
 

I think the problem is not in the replaced f.__doc__.

 
def MIGHT_FAIL(f, MSG, *k, **h):
     
# use MSG to determine whether  to invoke f or not 
# and do an error catch  here
     ....
     def innner(f): .....
     ......
     # get the right info of  f here for any trapped error   
     #return inner, result
     return inner
          
    

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Re: Python presentations Jean-Michel Pichavant <jeanmichel@sequans.com> - 2012-09-13 19:54 +0200
  Re: Python presentations Alister <alister.ware@ntlworld.com> - 2012-09-13 18:18 +0000
  Decorators not worth the effort alex23 <wuwei23@gmail.com> - 2012-09-13 18:58 -0700
    Re: Decorators not worth the effort Cameron Simpson <cs@zip.com.au> - 2012-09-14 12:12 +1000
      Re: Decorators not worth the effort alex23 <wuwei23@gmail.com> - 2012-09-13 20:25 -0700
    Re: Decorators not worth the effort Dieter Maurer <dieter@handshake.de> - 2012-09-14 08:40 +0200
    Re: Decorators not worth the effort Terry Reedy <tjreedy@udel.edu> - 2012-09-14 16:29 -0400
      Re: Decorators not worth the effort Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2012-09-15 09:13 +0200
      Re: Decorators not worth the effort alex23 <wuwei23@gmail.com> - 2012-09-16 17:38 -0700
    Re: Decorators not worth the effort Terry Reedy <tjreedy@udel.edu> - 2012-09-14 16:31 -0400
    Re: Decorators not worth the effort Terry Reedy <tjreedy@udel.edu> - 2012-09-14 16:37 -0400
      Re: Decorators not worth the effort 88888 Dihedral <dihedral88888@googlemail.com> - 2012-09-18 16:47 -0700
      Re: Decorators not worth the effort 88888 Dihedral <dihedral88888@googlemail.com> - 2012-09-18 16:47 -0700
    Re: Decorators not worth the effort Terry Reedy <tjreedy@udel.edu> - 2012-09-14 16:33 -0400
    Re: Decorators not worth the effort Ian Kelly <ian.g.kelly@gmail.com> - 2012-09-14 15:16 -0600
      Re: Decorators not worth the effort Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-14 23:39 +0000
        Re: Decorators not worth the effort 88888 Dihedral <dihedral88888@googlemail.com> - 2012-09-15 02:45 -0700
          Re: Decorators not worth the effort Dwight Hutto <dwightdhutto@gmail.com> - 2012-09-15 06:04 -0400
            Re: Decorators not worth the effort 88888 Dihedral <dihedral88888@googlemail.com> - 2012-09-15 07:18 -0700
              Re: Decorators not worth the effort Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2012-09-18 14:16 +0200
            Re: Decorators not worth the effort 88888 Dihedral <dihedral88888@googlemail.com> - 2012-09-15 07:18 -0700
    Re: Decorators not worth the effort Dwight Hutto <dwightdhutto@gmail.com> - 2012-09-14 23:42 -0400
    Re: Decorators not worth the effort "Dieter Maurer" <dieter@handshake.de> - 2012-09-15 08:31 +0200

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