[Python-3000] Iterators for dict keys, values, and items == annoying :)

[Greg Ewing]

Guido van Rossum wrote:

> But do we really want this? It's a pretty serious change in basic
> semantics of collection data types, *and* it requires us to find a way
> to determine unequivocally whether something is a set,  sequence,
> mapping, or multiset (and it can't be more than one!).

If we *did* want it, I think there would have to be a
collection of abstract types -- SequenceBase, MappingBase,
SetBase, etc., that all types wanting to participate in
this scheme would have to be based on. Since this would
go against duck typing, my feeling is no, we don't
want it.

If it's okay for lists and tuples containing the same
items to be unequal even though they're both sequences,
then I think it's okay for a real set not to be equal
to a set view of something.

If you really want to be able to compare different
set-like objects, there could be a function for that.
Or even a bunch of functions for doing set operations
on set-like objects.

There's a precedent for this in Numeric. The Numeric
array objects know how to do arithmetic with each
other, but there is also a set of functions add(),
multiply(), etc. which do the corresponding things
with any objects that can be treated as sequences
of sequences. It could be worth having a set of
functions like this in the core for doing sequence
operations, set operations, etc.

--
Greg