Decorators not worth the effort
88888 Dihedral
dihedral88888 at googlemail.com
Sat Sep 15 10:18:18 EDT 2012
David Hutto於 2012年9月15日星期六UTC+8下午6時04分28秒寫道:
> On Sat, Sep 15, 2012 at 5:45 AM, 88888 Dihedral
>
> <dihedral88888 at googlemail.com> wrote:
>
> > 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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> >>
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> >>
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> >> > If only there were a conceptually simpler way to do this. Actually,
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> >>
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> >> > there is. I give you: muman than humanetadecorators!
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> >>
>
> >> [code snipped but shown below]
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> >>
>
> >> > Which I think is certainly easier to understand than the nested
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> >>
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> >> > functions approach.
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> >>
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> >>
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> >>
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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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> >>
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> >> is supposed to work! At a quick glance, I would have sworn that it
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> >>
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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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> >>
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> >>
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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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> >>
>
> >> ...
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> >>
>
> >> py> @make_wrapper
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> >>
>
> >> ... def simple_decorator(func, *args, **kwargs):
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> >>
>
> >> ... print "Entering decorated function"
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> >>
>
> >> ... result = func(*args, **kwargs)
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> >>
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> >> ... print "Exiting decorated function"
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> >>
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> >> ... return result
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> >>
>
> >> ...
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> >>
>
> >> py> @simple_decorator
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> >>
>
> >> ... def my_function(a, b, c):
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> >>
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> >> ... """Doc string"""
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> >>
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> >> ... return a+b+c
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> >>
>
> >> ...
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> >>
>
> >> py> my_function(1, 2, 3)
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> >>
>
> >> Entering decorated function
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> >>
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> >> Exiting decorated function
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> >>
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> >> 6
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> >>
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> >>
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> >>
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> >> So to me, this is far more magical than nested functions. If I saw this
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> >>
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> >> in t requires me to hunt through your library for the "simple function
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> >>
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> >> buried in a utility module somewhere" (your words), instead of seeing
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> >>
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> >> everything needed in a single decorator factory function. It requires
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> >>
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> >> that I understand how partial works, which in my opinion is quite tricky.
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> >>
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> >> (I never remember how it works or which arguments get curried.)
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> >>
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> >>
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> >>
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> >> And the end result is that the decorated function is less debugging-
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> >>
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> >> friendly than I demand: it is an anonymous partial object instead of a
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> >>
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> >> named function, and the doc string is lost. And it is far from clear to
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> >>
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> >> me how to modify your recipe to use functools.wraps in order to keep the
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> >>
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> >> name and docstring, or even whether I *can* use functools.wraps.
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> >>
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> >>
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> >>
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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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> >>
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> >> is *inherently* more understandable than the standard decorator approach:
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> >>
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> >>
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> >>
>
> >> def simple_decorator2(func):
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> >>
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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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> >>
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> >>
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> >>
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> >> This is no more complex than yours, and it keeps the function name and
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> >>
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> >> docstring.
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> >>
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> >>
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> >>
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> >>
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> >>
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> >> > Parameterized decorators are not much more
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> >>
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> >> > difficult this way. This function:
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> >>
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> >> [snip code]
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> >>
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> >> > And now we have a fancy parameterized decorator that again requires no
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> >>
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> >> > thinking about nested functions at all.
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> >>
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> >>
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> >>
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> >> Again, at the cost of throwing away the function name and docstring.
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> >>
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> >>
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> >>
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> >> I realise that a lot of this boils down to personal preference, but I
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> >>
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> >> just don't think that nested functions are necessarily that hard to
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> >>
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> >> grasp, so I prefer to see as much of the decorator logic to be in one
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> >>
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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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>
>
> Like chi fu, allow decorators to evolve upon themselves. Like simple
>
> moves flow through water and allow memorization of activity through
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> evidence of existence.
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>
>
>
>
> --
>
> Best Regards,
The concept of decorators is just a mapping from a function to another
function with the same name in python.
It should be easy to be grapsed for those studied real analysis and
functional analysis.
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