[Python-Dev] Proposed tweaks to functools.wraps

[Eric Snow]

Actually, what is the problem with having all decorators add a __decorated__ to the function that ultimately gets returned, pointing to the function they decorated?  I guess I never saw that discussion.  Perhaps set it to None when the decorator is the same as the decorated (no wrapping involved).  The alternative is sifting through closures, trying to figure out which is the decorated function.  Finding the original decorated function has been a real pain, particularly when a function has more than one closure cell.

-eric

-----Original Message-----
From: python-dev-bounces+esnow=verio.net at python.org [mailto:python-dev-bounces+esnow=verio.net at python.org] On Behalf Of Nick Coghlan
Sent: Tuesday, August 10, 2010 8:31 PM
To: python-dev at python.org
Subject: [Python-Dev] Proposed tweaks to functools.wraps

Based on a pair of tracker issues (#3445 and #9396) I'm considering a
couple of adjustments to functools.wraps for 3.2.

The first (#3445) is a request from ages ago to make update_wrapper
more forgiving when it encounters a missing attribute. Instead of
throwing AttributeError (as it does now), it would just skip the
missing attribute. This would allow wraps to be used with other
callables that don't fully mimic the function API. I was initially
opposed to the idea, but over time I've come to think this is a case
where practicality beats purity (since that really sums up
functools.wraps in general - it is already the case that the copied
info isn't quite right for the decorated function, but it's still
better than using the wrapper function's own metadata).

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. Some time back, we
considered doing this automatically as an integral part of decoration,
but decided that wasn't appropriate. However, building it into the
explicit wrapping functions makes sense to me. To avoid namespace
conflicts, I plan to use "__wraps__" as the name for the reference to
the original function.

Thoughts? Concerns? Better ideas?

Cheers,
Nick.

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