[Python-Dev] Getting rid of unbound methods: patch available

[M.-A. Lemburg]

Nick Coghlan wrote:
> Guido van Rossum wrote:
> 
>> What do people think? (My main motivation for this, as stated before,
>> is that it adds complexity without much benefit.)
> 
> 
> I'm in favour, since it removes the "an unbound method is almost like a 
> bare function, only not quite as useful" distinction. It would allow 
> things like str.join(sep, seq) to work correctly for a Unicode 
> separator. 

This won't work. Strings and Unicode are two different types,
not subclasses of one another.

> It also allows 'borrowing' of method implementations without 
> inheritance.
 >
> I'm a little concerned about the modification to pyclbr_input.py, though 
> (since it presumably worked before the patch). Was the input file 
> tweaked before or after the test itself was fixed? (I'll probably get 
> around to trying out the patch myself, but that will be on Linux as 
> well, so I doubt my results will differ from yours).
> 
> The other question is the pickling example - an unbound method currently 
> stores meaningful data in im_class, whereas a standard function doesn't 
> have that association. Any code which makes use of im_class on unbound 
> methods (even without involving pickling)is going to have trouble with 
> the change. (Someone else will need to provide a real-life use case 
> though, since I certainly don't have one).

I don't think there's much to worry about. At the C level,
bound and unbound methods are the same type. The only
difference is that bound methods have the object
attribute im_self set to an instance object, while
unbound methods have it set NULL.

Given that the two are already the same type, I don't
really see much benefit from dropping the printing of
"unbound" in case im_self is NULL... perhaps I'm missing
something.

As for real life examples: basemethod() in mxTools uses
.im_class to figure the right base method to use (contrary
to super(), basemethod() also works for old-style classes).
basemethod() in return if used in quite a few applications
to deal with overriding methods in mixin classes.

-- 
Marc-Andre Lemburg
eGenix.com

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