On Sat, Sep 15, 2012 at 5:45 AM, 88888 Dihedral <dihedral88...@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 -- http://mail.python.org/mailman/listinfo/python-list
