[Python-Dev] copy confusion

[Guido van Rossum]

> Unfortunately, we do have a problem with the code in copy.py:
> 
> class MetaCopyableClass(type):
>      def __copy__(cls):
>          """ code to copy CLASSES of this metaclass """
>      # etc, etc, snipped
> 
> class CopyableClass:
>      __metaclass__ = MetaCopyableClass
>      # rest of class snipped
> 
> x = CopyableClass()
> 
> import copy
> y = copy.copy(x)
> 
> kallisti:/tmp alex$ python x.py
> Traceback (most recent call last):
>    File "x.py", line 14, in ?
>      y = copy.copy(x)
>    File "/usr/local/lib/python2.4/copy.py", line 79, in copy
>      return copier(x)
> TypeError: __copy__() takes exactly 1 argument (2 given)
> kallisti:/tmp alex$
> 
> See?  copy.copy(x) ends up using MetaCopyableClass.__copy__ -- because
> of a getattr on CopyableClass for '__copy__', which gets the
> BOUND-METHOD defined in the metaclass, with im_self being
> CopyableClass.
> 
> I had exactly the same metabug in the pep 246 reference implementation,
> Armin Rigo showed how to fix it in his only recent post.

Don't recall seeing that, but if you or he can fix this without
breaking other stuff, it's clear you should go ahead. (This worked in
2.2, FWIW; it broke in 2.3.)

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)