Decorators not worth the effort

[88888 Dihedral]

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:
> 
> >>
> 
> >>
> 
> >>
> 
> >> > 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,


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.