list IndexError

[Alex Martelli]

Scott David Daniels <Scott.Daniels at Acm.Org> wrote:

> Ishwor wrote:
> > On Thu, 23 Dec 2004 13:57:55 -0300, Batista, Facundo
> > <FBatista at unifon.com.ar> wrote:
> >>#- True, true.  Maybe you could lobby for copy as a builtin in 
> >>#- Python 3000? 
> >>
> >>That's a good idea to me. But copy() as a builtin is not clear if it's
> >>shallow or deep. 
> > 
> > IMHO its preferable to use shallow one as the built-in because deep is
> > expensive op. for CPU. ~;-)
> "deepcopy" is an operation that is less well defined than shallow copy
> anyway (and hence shouldn't be a default).  Objects representing
> constants may contain a cache (for example) as an efficiency measure,
> and "deepcopy" needn't copy such objects.  The only way to safely
> do deepcopy is to copy down to immutables, but usually there is a
> shallower and faster implementation that depends on application
> semantics.

Well, that's what methods __copy__ and __deepcopy__, or the
often-preferable __getstate__ and __setstate__, are all about -- letting
your classes explicitly define what IS the state (that needs to be
copied) of their instances.  I don't see how that changes between
copy/deepcopy being built-ins or being in a standard library module like
today.  Yes, deep copy is way more involved and expensive that shallow
copy, etc, etc, but, again, this holds whether they're built-ins or come
from a standard library module.

I guess I must be missing something...?


Alex