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