Add support for PEP 750 template strings

[1borgy]

For reviewers

• I did not use AI
• I used AI and thoroughly reviewed every code/docs change

Description of the change

Add expressions for ast.TemplateStr and ast.Interpolation, which were added in Python 3.14. Round-tripping (e.g. tests/test_expressions.py::test_expressions) does not work with the conversion or format_spec fields, though this is consistent with the current implementation of ExprJoinedStr and ExprFormatted.

Relevant resources

• https://peps.python.org/pep-0750/
• https://docs.python.org/3/library/ast.html#ast.TemplateStr
• https://docs.python.org/3/library/ast.html#ast.Interpolation

[1borgy]

Looks like most of CI is passing, bar config/test_api.py::test_api_matches_inventory for python<3.14. The suggestion of make run mkdocs build did not generate any changes to site/objects.inv for me. For the sake of not overusing GHA runner resources, I'll wait for a maintainer's blessing before investigating further.

[pawamoy]

Thanks @1borgy, super clean! Just a few comments.

[pawamoy]

Are we sure that using hardcoded single (or double) quotes will work in every case? 🤔

[1borgy]

I referred to the implementation of ExprJoinedStr for this. As far as I can tell, this iterate method is only used when round-tripping in tests or dumping expressions by __str__ - it doesn't seem like it's very critical? Please correct me if I misunderstand.

I imagine this round-tripping could break when strings contain certain types of quotes - for example, if input value is t"a'b", converting this to t'a'b' would invalidate syntax. However, if we have the same problem with ExprJoinedStr and ExprTemplateStr, I propose creating a new project issue to improve quote handling.

[pawamoy]

It's critical: it must yield correct code. This code is then parsed to be highlighted, formatted etc. by Black/Ruff/Pygments/else in downstream tools like mkdocstrings-python.

However, if we have the same problem with ExprJoinedStr and ExprTemplateStr, I propose creating a new project issue to improve quote handling.

You make a good point. Lets handle that in a new issue then 🙂

[pawamoy]

Looks like most of CI is passing, bar config/test_api.py::test_api_matches_inventory for python<3.14. The suggestion of make run mkdocs build did not generate any changes to site/objects.inv for me.

Oh we probably just need to add the two new classes ExprInterpolation and ExprTemplateStr to docs/reference/api/expressions.md.

[1borgy]

Thanks @1borgy, super clean! Just a few comments.

Thanks for the review! Looks like most of CI is passing now, bar the 3.15 tests bombing out. Let me know how you'd like to move forward ^^

[pawamoy]

Yep, failures on 3.15 are fine, I'll investigate them later 🙂 Let me know when you think this is ready to merge!

[pawamoy]

Thanks again!