[Python-Dev] Add a frozendict builtin type

[Alex Gaynor]

Nick Coghlan <ncoghlan <at> gmail.com> writes:

> I'm pretty sure the PyPy jit can already pick up and optimise cases
> where a dict goes "read-only" (i.e. stops being modified).

No, it doesn't. We handle cases like a type's dict, or a module's dict,
by having them use a different internal implementation (while, of course,
still being dicts at the Python level). We do *not* handle the case of
trying to figure out whether a Python object is immutable in any way.

Alex