Use sys.version_info to guard imports

[alicederyn]

Pull Request Checklist

• Fixes #
• Tests added
• Documentation/examples added
• Good commit messages and/or PR title

Description of PR
Currently, conditional imports that depend on Python version are using try/except ImportError to import from typing_extensions on older Python versions. This is not natively supported by typecheckers, forcing use of error suppression, and losing potential validation of downstream code. (Additionally, pyright is erroneously flagging a lot of code that uses Annotated with "Call expression not allowed in type expression, making it harder to spot real issues in VSCode.)

This PR refactors these conditional imports to use the recommended if sys.version_info >= (3, minor): pattern instead.

See also: mypy issue comment, pyright issue comment

[alicederyn]

The old version of this code was importing Self in the try/except block, causing it to fall back to the bespoke implementation in typing_extensions for Python 3.9. I'm unclear if this was intentional, so retained this behaviour to avoid any potential regression. For Python 3.10, typing_extensions imports Python's built-in version, so we can import it directly.

[alicederyn]

Unclear if this was intentionally not guarded, so left as-is. If the intention is to ensure any future typing_extensions behavioural changes are included, we could in a future PR change this to

if TYPE_CHECKING:
  if sys.version_info >= (3, 9):
    from typing import ParamSpec, get_args, get_origin
  else:
    from typing_extensions import ParamSpec, get_args, get_origin
else:
  try:
    # Prefer to use get_args/get_origin from typing_extensions to support any future behavioural
    # extensions
    from typing_extensions import ParamSpec, get_args, get_origin
  except ImportError:
    # Fall back to typing if typing_extensions is not available
    from typing import ParamSpec, get_args, get_origin

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.5%. Comparing base (d553546) to head (90a7a2e).
Report is 190 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1177     +/-   ##
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- Coverage   81.7%   81.5%   -0.2%     
=======================================
  Files         54      60      +6     
  Lines       4208    4756    +548     
  Branches     889    1016    +127     
=======================================
+ Hits        3439    3880    +441     
- Misses       574     646     +72     
- Partials     195     230     +35     

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[jeongukjae]

👍

[jeongukjae]

Not strong opinion. looks great if we update this statement as well.

[alicederyn]

👍 Will leave to a separate PR to avoid risking coupling a behaviour change to a large refactor