Add comment indicating default value of format parameter in typing.get_type_hints()

[Viicos]

The runtime definition only has a default of None to lazily import annotationlib: https://github.com/python/cpython/blob/66e1399311c17684c6e26f5d9d9603fbd0717d0d/Lib/typing.py#L2365-L2367.

While providing None explicitly is technically valid, it's best to have the value present in the stub so that users can easily know the default value.

[srittau]

This needs stubtest allowlist entries.

[JelleZijlstra]

I'd prefer to keep None because that's the actual runtime default, regardless of the motivation.

[Viicos]

I'd find it a bit unfortunate but I don't have strong opinions. I'm wondering if None should in fact not be documented at all, so that if the lazy loading of the annotationlib module goes away, it can be switched back without maintaining backwards compatibility for None.

Or, could we at least have a comment in the stubs stating what is the actual default?

[srittau]

Or, could we at least have a comment in the stubs stating what is the actual default?

That sounds like a good compromise to me.

[JelleZijlstra]

A comment would be fine!

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉