Hey Nick,

Sorry for the long delay. Unfortunately Python isn't my main work language anymore so working on this has proved to be quite a context switch. I'm going to try to finish this up now.

The attached patch implements a new pattern for wrapping runpy - one that I hope is a bit more general than just setting argv. In particular, using the new load_module/load_path doesn't automatically change argv at all when calling run. The callers can do pretty much whatever they want before calling run().

From a docs perspective this is quite a bit easies to understand. You call runpy.load_* to find the module, change whatever you want: globals/module dict values/names/etc, and call .run(). We would even expose a convenient `with runpy.ModifiedArgv(argv):` to help with the argv swapping. "Simple" use-cases can continue to use runpy.run_* without needing to get into the save/restore we do here.

Let me know what you think of this approach and I can flesh out the docs around it. Otherwise, I'm more than happy to implement the callback approach you suggested.

Thanks,
Mike.