Challenge supporting custom deepcopy with inheritance

[Aahz]

In article <mailman.1077.1244061915.8015.python-list at python.org>,
Michael H. Goldwasser  <goldwamh at slu.edu> wrote:
>On  June 2, 2009, Aahz wrote: 
>>Michael Goldwasser:
>>>
>>>class A(object):
>>>    def __init__(self, aTag):
>>>        self.__aTag = aTag
>>>        self.__aList = []
>>    
>>    IMO, your problem starts right here.  Not only are you using customized
>>    attributes for each class, you're using class-private identifiers.  You
>>    would vastly simplify your work if you switch to single-underscore
>>    attributes.
>
>  I intentionally chose the class-private identifiers in my artificial
>  example to emphasize that I was looking for a solution in which
>  class B did not have to rely on particular knowledge of class A's
>  implementation.  That said, switching to single-underscores does not
>  address the issue raised in the original post.

Not directly, but it does simplify possible solutions.  For example, you
could use a straightforward getattr() approach where the class contains
an attribute listing all the deep-copyable attributes.  You could even
use name-munging so that attributes can have an accompanying
ATTR_deepcopy() method for custom code so that your main __deepcopy__
method stays the same in subclasses.

(Obviously, this trick does in fact still work if you use private
attributes and do the name-mangling yourself, but I find that distasteful
for production code unless it's absolutely required.)
-- 
Aahz (aahz at pythoncraft.com)           <*>         http://www.pythoncraft.com/

"Given that C++ has pointers and typecasts, it's really hard to have a
serious conversation about type safety with a C++ programmer and keep a
straight face.  It's kind of like having a guy who juggles chainsaws
wearing body armor arguing with a guy who juggles rubber chickens wearing
a T-shirt about who's in more danger."  --Roy Smith, c.l.py, 2004.05.23