[Python-Dev] advice needed: best approach to enabling "metamodules"?

[Antoine Pitrou]

On Sat, 29 Nov 2014 01:59:06 +0000
Nathaniel Smith <njs at pobox.com> wrote:
> 
> Option 1: Make it possible to change the type of a module object
> in-place, so that we can write something like
> 
>    sys.modules[__name__].__class__ = MyModuleSubclass
> 
> Option 1 downside: The invariants required to make __class__
> assignment safe are complicated, and only implemented for
> heap-allocated type objects. PyModule_Type is not heap-allocated, so
> making this work would require lots of delicate surgery to
> typeobject.c. I'd rather not go down that rabbit-hole.

Option 1b: have __class__ assignment delegate to a tp_classassign slot
on the old class, so that typeobject.c doesn't have to be cluttered with
many special cases.

> Option 3: Make it legal to assign to the __dict__ attribute of a
> module object, so that we can write something like
> 
>    new_module = MyModuleSubclass(...)
>    new_module.__dict__ = sys.modules[__name__].__dict__
>    sys.modules[__name__].__dict__ = {}     # ***
>    sys.modules[__name__] = new_module
> 
[...]
> 
> Option 4: Add a new function sys.swap_module_internals, which takes
> two module objects and swaps their __dict__ and other attributes. By
> making the operation a swap instead of an assignment, we avoid the
> lifecycle pitfalls from Option 3. By making it a builtin, we can make
> sure it always handles all the module fields that matter, not just
> __dict__. Usage:

How do these two options interact with the fact that module functions
store their globals dict, not the module itself?

Regards

Antoine.