Handle subscripted generics in query selector

[davetapley]

Same as #3805 but change my branch off main

[rodrigogiraoserrao]

Hey Dave, thanks for the PR.
Would you mind adding a couple of regression tests? 🙌

[davetapley]

@rodrigogiraoserrao I can but it won't be pretty because:

The fix requires Python 3.9 (for https://peps.python.org/pep-0585/), but the tests also run on 3.8.

Note: #2867 is a hard crash anyway, so fix is no worse than existing behavior on 3.8.

For tests can either:

1. Defer until 3.8 support is dropped (easiest)
2. Only run test on >= 3.9
3. Expect exception on 3.8, work on >= 3.9

Any preference?

[rodrigogiraoserrao]

Hey Dave,

Maybe I misunderstood what you're saying but are you suggesting that adding a couple of regression tests and marking them with a @skipif that checks if we're on Python 3.9+ is ugly?

I agree that the new change is no worse than the current behaviour and thus I'm personally a fan of this change but we typically don't add new features without tests!

[davetapley]

@rodrigogiraoserrao I was, but I didn't know about skipif, that makes it look quite easy 😁
I'll get some tests in ASAP.

[willmcgugan]

Would I be correct in saying this wouldn't check the generic type, just the class?

i.e. the following would return all DataTable, not just float Datatables?

self.query("*", "DataTable[float]")