Method returning new instance of class?

[Arthur]

"Martin v. Löwis" <martin at v.loewis.de> wrote in message
news:4139a87a$0$30204$9b622d9e at news.freenet.de...
> Arthur wrote:
> > Essentially I am trying to create a non-destructive tranformation of an
> > instance of a class - is one way of putting it.
> >
> > The way I am currently conceptualizing a solution, what I need is a
method
> > of the class that returns a new instance of the class.
>
> So you want a copy of the object. I'd use copy.copy for this, perhaps
> copy.deepcopy.

That was my first instinct.  And perhaps my problem is in here somewhere.

The app is graphical, and I use a Python extensions in C++ using the Boost
library (vpython, new version).  My class instance has an attribute which is
a vpython object. Copy.copy doesn't get me where I need to be because my new
instance gets a reference to the same vpython object, and changes to it are
reflected in the original instance. Copy.deepcopy doesn't work for more
obscure reasons.  I get an error message generating up from vpython when I
try to change an attribute of the object on the new instance  - though I am
interacting with it in the same manner that works fine when performed on the
original instance.

But do you see any reason why this might be?

If it sounds totally illogical, I'll go back and check myself - because of
course the actual sitruation is a bit more complicated than what I am
describing, and I guess it is possible I am falling off the ledge somewhere
else.

Art
>
> Regards,
> Martin