Dictionary .keys() and .values() should return a set[withPython3000 in mind]

[Delaney, Timothy (Tim)]

Scott David Daniels wrote:

> Delaney, Timothy (Tim) wrote:
>> Plus copy-on-write isn't something you want in general - it's *much*
>> slower since it needs to copy the internal data every time it's
>> modified. The vast majority of uses of data structures does not
>> involve concurrent modification.
> 
> But copy-on-write in the presence of reference counts doesn't do the
> mad useless-copy stuff.

Good point - if there's only one reference, there's no need for copying
- this is definitely something that could be taken advantage of.

Tim Delaney