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

[Greg Ewing]

Brett Cannon wrote:

> Basically a simple
> set interface where we could have a __container__/__view__/__set__
> whatever method to call to get a view of the data structure. 
> Basically a read-only (with a possible delete possibility) mapping
> interface.

If there's an obvious default meaning for the basic access
methods like __contains__ and __len__, there's no need for
a view to provide these -- the original object can (and
should) just implement them itself.

Views only come into play when there is more than one
possible view of an object (e.g. dict has keys, items,
values). Then the details are completely type-specific.

There might be room for a general immutable view object
that doesn't allow any changes, but that could be
provided as a generic wrapper that doesn't need to know
anything about the base object or vice versa.

> Without a direct reason in terms of the language needing a
> standardization of an interface, perhaps we just don't need
 > views.

On the contrary, views are a very useful idea, *as a
design pattern*. What we *don't* need in Python, as far
as I can see, is any formalised protocols or interfaces
for views, because there's nothing that can be said about
them in general.

Thinking that "having views" means "having a formally
defined interface for views" is a mindset that comes
from B&D languages like Java. It doesn't apply to
Python at all.

--
Greg