Semi-newbie, rolling my own __deepcopy__

[Michael Spencer]

ladasky at my-deja.com wrote:
...
I see Steve Bethard has answered most of the points in your last eMail

> On line 11 we create a
> dictionary item in memo, [id(self):type(self)]...So now I'm confused as
> to the purpose of memo.  Why should it contain the ID of the *original*
> object?

No, you create memo[id(self):type(self)()] i.e., a mapping of the old object to 
a new object of the same type.  This new object does not yet contain the data of 
the old one, because you called its __init__ method with no arguments.

BTW, as I mentioned in a previous comment, I believe this would be more plainly 
written as type(self).__new__(), to emphasize that you are constructing the 
object without initializing it.  (There is a explanation of __new__'s behaviour 
at http://www.python.org/2.2/descrintro.html#__new__).  This works only for 
new-style classes (also explained in the same reference).  For old-style 
'classic' classes you would use new types.InstanceType

...
> 
> Is there another section of the Python docs that will clarify all this
> for me?  I got hung up on all the "static", "public", etc. declarations
> in Java early on.  Python has taken me an awful lot farther, but
> perhaps I'm hitting the conceptual wall again.

I assume you have seen http://docs.python.org/lib/module-copy.html which 
explains this topic and, in particular, why the memo dict is passed around.

Hang in there.  It's not an easy topic, and this example contains several 
subtleties as you have discovered.

If you want further help, why not post the actual class you are working with, 
and your __deepcopy__ attempt.  It would be much easier to react to something 
concrete than a general howto.

Michael