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

[Greg Ewing]

Delaney, Timothy (Tim) wrote:

> This whole discussion suggests to me that what would be best is if we
> defined an actual "view" protocol, and various builtins return views,
> rather than either copies or iterators.

I'm not sure that any formal protocol is needed. Each
container will be providing its own set of methods for
producing views, and each of the views will behave in
ways specific to the type that it's viewing. I can't
see there being a place for anything like the __iter__
slot for views. Each case will be unique.

> A view provides the same access methods, etc as the object it is backed
> by.

They can't be *exactly* the same, or there would be no
point in having a view in the first place.

> The aim of a view is to be lightweight.

Agreed.

> A view should not allow modification of the underlying object

I think I agree with that, at least in the cases where
we're changing an existing method (e.g. dict.keys()) that
used to return an independent object. Then code which is
expecting the old semantics will fail fairly obviously.

Greg