fix: Invalid selectors not being recognized

[pavelzw]

Closes #19023

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.51%. Comparing base (1f48036) to head (3947452).
Report is 43 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #19136      +/-   ##
==========================================
- Coverage   79.78%   79.51%   -0.28%     
==========================================
  Files        1531     1527       -4     
  Lines      208427   209204     +777     
  Branches     2913     2415     -498     
==========================================
+ Hits       166295   166345      +50     
- Misses      41581    42311     +730     
+ Partials      551      548       -3     

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[ritchie46]

Whys does mypy complain here?

[pavelzw]

❯ mypy py-polars/tests/unit/test_selectors.py
py-polars/tests/unit/test_selectors.py:822: error: Argument 1 to "drop" of "DataFrame" has incompatible type "Expr"; expected "str | _selector_proxy_ | Iterable[str | _selector_proxy_]"  [arg-type]
py-polars/tests/unit/test_selectors.py:824: error: Argument 1 to "drop" of "DataFrame" has incompatible type "Expr"; expected "str | _selector_proxy_ | Iterable[str | _selector_proxy_]"  [arg-type]
Found 2 errors in 1 file (checked 1 source file)

[ritchie46]

Then I think we must pass a seelctor as we don't allow expression inputs here.

[pavelzw]

i could reproduce the issue as well with the following:

pl.selectors.all() + pl.col("x")

which is at runtime a _selector_proxy_, mypy still thinks it's a Expr, hence the assert in 3947452 (#19136)