Copy with __slots__

[Alex Martelli]

Antonio Cuni wrote:

> Griebel, Peer wrote:
> 
>> So my advice now is: Use slots! The program runs faster, uses less
>> memory. And explicitly coding a __copy__ function which copies each
>> attribute isn't a bad thing per se. It makes the things more explicit.
> 
> (sorry for my bad english...)

English excellent, Python less so:-) (...just kidding...)

 
> we can make it easier by providing a metaclass that creates a __copy__
> method for us:
> 
> class autocopy(type):
>     def __new__(cls, name, bases, dic):
>         def __copy__(self):
>             res = self.__class__()
>             for attr in dic['__slots__']:
>                 setattr(res, attr, getattr(self, attr))
>             return res
> 
>         dic['__copy__'] = __copy__
>         return type.__new__(cls, name, (object,), dic)

This doesn't deal with inherited __slots__.  Easy to solve,
mind you -- autocopy.__new__ just needs to look for __slots__
in the bases, too, and accumulate them all into a sequence
on which the nested __copy__ function can loop.  Some care
is needed, though (I can think of several possible anomalies).


Alex