Decorators not worth the effort

[Dwight Hutto]

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:
>>
>>
>>
>> > If only there were a conceptually simpler way to do this.  Actually,
>>
>> > there is.  I give you: muman than humanetadecorators!
>>
>> [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.

Like chi fu, allow decorators to evolve upon themselves. Like simple
moves flow through water and allow memorization of activity through
evidence of existence.


-- 
Best Regards,
David Hutto
CEO: http://www.hitwebdevelopment.com