[Python-Dev] Proposed tweaks to functools.wraps

[Nick Coghlan]

On Wed, Aug 11, 2010 at 12:48 PM, Éric Araujo <merwok at netwok.org> wrote:
>> The second (#9396) came up in the context of the new cache decorators
>> added to functools, and allowing applications to choose their own
>> caching strategies. I suggested exposing the original (uncached)
>> function, and Raymond suggested that the easiest way to enable that
>> would be for functools.update_wrapper to add a new attribute that
>> provides a reference to the original function.
>
> I moved this feature request to its own bug after brief IRC discussion
> with RDM: http://bugs.python.org/issue9567
>
> The idea was to separate concerns and eventually get feedback from
> people reading new-bugs-announce, but your email actually does that :)
>
> I say “add attribute to partial objects” in the bug title since I don’t
> know if it’s feasible in wraps only; while update_wrapper is simple
> Python code, wraps merely delegates to _functools.partial, so please
> change the title (and maybe add easy keyword) if appropriate.

Ah, that's the trick though - the partial object is the *decorator*,
so when you write

@wraps(f)
def wrapper:
   # ....

it is equivalent to:

def wrapper:
   # ....

wrapper = partial(update_wrapper, wrapped=f)(wrapper)

The partial object is a transient thing during the decoration process
- the wrapper function itself is the object that persists.

So it's only update_wrapper that needs changing to add the new attribute.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia