[Tutor] Challenge supporting custom deepcopy with inheritance

[Kent Johnson]

On Sun, May 31, 2009 at 5:35 PM, Michael H. Goldwasser <goldwamh at slu.edu> wrote:
>
> Yesterday, I posted a question to python-list involving custom
> deepcopies in an inheritance hierarchy.  I haven't received any
> responses, so I thought I'd cross-post to see if anyone on tutor
> has any thoughts.
>
> To avoid splitting the thread, I'll simply reference the original post at
> http://mail.python.org/pipermail/python-list/2009-May/714866.html
> and ask for responses to be sent there.

Sorry, splitting the thread for you...

ISTM that in general B.__deepcopy__() should call A.__deepcopy__() to
do the "A" part of the work. In your example, this won't work because
A.__deepcopy__() assumes that subclasses have a one-argument
constructor. So, I would say that B is not fulfilling the contract
assumed by A.

What if you give B a one-arg constructor by making the bTag argument
optional? Then I think B.__deepcopy__() can call A.__deepcopy__(),
then do the "B" part of the copy on the result.

Kent