add __builtins__ to globals in py.run() if they're missing

[GoldsteinE]

Python code doesn't like to run without __builtins__, so adding them if missing seems to be a good idea. Also that's what CPython >3.10 does.

See python/cpython#24564
Resolves #3370

• Agreed to dual-license (Dual-license PyO3 under Apache 2.0 or MIT #3108 (comment))
• Entry in newsfragments
• Tests for changed functions

[davidhewitt]

Many thanks, implementation looks great. My only thought: after evaluation should we attempt to remove __builtins__ from the globals dictionary if we added it?

[davidhewitt]

👍

[GoldsteinE]

Many thanks, implementation looks great. My only thought: after evaluation should we attempt to remove builtins from the globals dictionary if we added it?

I think that’s more confusing than the current option (especially given possibility of code like __builtins__ = new_value). CPython uses some private APIs to specify __builtins__ for the new frame explicitly instead of adding them to globals, so we can’t easily mimic its behaviour here (in particular, we’d need _PyFunction_FromConstructor: I don’t see a way to manually specify __builtins__ otherwise).

[davidhewitt]

Agreed, in which case I think let's just document that globals will be modified in this way (on both Python::run and Python::eval) and call it a day.

[GoldsteinE]

Fixed the docs.

[davidhewitt]

Thanks again!