[Python-Dev] (no subject)
Phillip J. Eby
pje at telecommunity.com
Mon Mar 14 16:28:50 CET 2005
At 05:34 AM 3/14/05 -0800, Michael Chermside wrote:
>Nice... thanks. But I have to ask: is this really the right set of metadata to
>be updating? Here are a few things that perhaps ought be copied by
> f.__name__ (already included)
> f.__doc__ (already included)
> f.__dict__ (already included)
> f.__module__ (probably should include)
> f.func_code.co_filename (to match f.__name__, but I'd leave it alone)
Leave __module__ alone, too, unless you want to play havoc with any
inspection tools looking for the source code.
>there's also the annoying fact that in IDLE (and in some other python-aware
>IDEs) one can see the argument signature for a function as a "tool tip"
>or other hint. Very handy that, but if a decorator is applied then all
>you will see is "func(*args, **kwargs)" which is less than helpful. I'm
>not sure whether this CAN be duplicated... I believe it is generated by
>examining the following:
> f.func_code.co_flags & 0x4
> f.func_code.co_flags & 0x8
>...and I suspect (experimentation seems to confirm this) that if you mangle
>these then the code object won't work correctly. If anyone's got a
>suggestion for fixing this, I'd love to hear it.
One solution is to have a __signature__ attribute that's purely
documentary. That is, modifying it wouldn't change the function's actual
behavior, so it could be copied with update_meta() but then modified by the
decorator if need be. __signature__ would basically be a structure like
the one returned by inspect.getargspec(). Also, 'instancemethod' would
have a __signature__ equal to its im_func.__signature__ with the first
argument dropped off, thus making it easy to introspect wrapper chains.
I discussed this approach with Guido in private e-mail a few months back
during discussion about an article I was writing for DDJ about
decorators. We also discussed something very similar to 'update_meta()',
but never settled on a name. Originally he wanted me to PEP the whole
thing, but he wanted it to include optional type declaration info, so you
can probably see why I haven't done anything on that yet. :)
However, if we can define a __signature__ format that allows for type
declaration, I imagine there'd be little problem with moving forward on it.
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