overloading *something

[sjdevnull at yahoo.com]

Robert Kern wrote:
> James Stroud wrote:
>
> > Does anyone else find the following annoying:
> >
> > py> from UserDict import UserDict
> > py> aud = UserDict({"a":1, "b":2})
> > py> def doit(**kwargs):
> > ...   print kwargs
>
> UserDict only exists for backwards compatibility with old code that used
> it before one could subclass from dict directly. Don't use it if you can
> avoid it. UserDict only ever exposed the Python-side interface of dicts.
> It couldn't expose the C-side interface, and it's the C-side interface
> that **kwds is using.

Which means that you can't subclass dict with, say, a lazy dictionary
(that doesn't retrieve values until they're looked up) and use it with
**kwargs.  That bit me last year:

http://groups.google.com/group/comp.lang.python/browse_frm/thread/95cfa91b732cd482/24b7e17bb395494e

It would be useful in some situations to be able to do this (especially
where getting the dictionary values is time-consuming and the function
you're calling doesn't use all the values in the dictionary).  For my
particular case I had a fairly easy workaround.