[Python-Dev] Add a frozendict builtin type

[Victor Stinner]

> A frozendict type is a common request from users and there are various
>> implementations. There are two main Python implementations:
>
> Perhaps this should also detail why namedtuple is not a viable alternative.

It doesn't have the same API. Example: frozendict[key] vs
namedtuple.attr (namedtuple.key). namedtuple has no .keys() or
.items() method.

Victor