fix: Improve error message for temporal vs non-temporal comparison

[sachinn854]

When comparing temporal dtypes (Date / Datetime / Duration / Time)
against non-temporal values, Polars previously raised:

"Series of type <dtype> does not have eq operator"

This error was misleading, because the operator does exist — the
comparison is simply invalid due to incompatible types.

This change improves the error message to explicitly state that a
temporal value is being compared against a non-temporal dtype, e.g.:

TypeError:
Invalid comparison between temporal dtype 'Date'
and non-temporal value of dtype <class 'int'>.
Temporal values may only be compared against
compatible temporal dtypes.

This makes the behavior clearer and more consistent with user
expectations when performing mixed-dtype comparisons.

Closes #25729

[Copilot]

Pull request overview

This PR improves the error message when comparing temporal dtypes (Date, Datetime, Duration, Time) with non-temporal values. Previously, the error was generic: "Series of type Date does not have eq operator". The new error is more descriptive: "Invalid comparison between temporal dtype Date and non-temporal value of dtype <class 'int'>. Temporal values may only be compared against compatible temporal dtypes."

Key changes:

• Added a specific error check for temporal vs non-temporal comparisons before falling back to the generic "does not have operator" error
• The check uses is_temporal() method to identify temporal dtypes and distinguish them from other types

---

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[Copilot]

The temporal dtype check should exclude None values. None/null values should be comparable with any dtype, including temporal dtypes. If the FFI function lookup fails for a None comparison, this check would incorrectly raise a TypeError categorizing None as a "non-temporal value". Add and other is not None to the condition on line 834 before checking if the other value is non-temporal.

Suggested change

	self.dtype.is_temporal()
	self.dtype.is_temporal()
	and other is not None

[Copilot]

This new error message should have test coverage to ensure it's raised correctly when comparing temporal dtypes (Date, Datetime, Duration, Time) with non-temporal scalar values (int, str, float, etc.). Consider adding tests that verify the error message is shown for each temporal dtype when compared with various non-temporal types.

[sachinn854]

The CI failures are coming from the delta-lake IO tests:

• tests/unit/io/test_delta.py::test_write_delta
• tests/unit/io/test_delta.py::test_scan_delta_loads_aws_profile_endpoint_url

They are related to file: vs file:// uri handling / S3 endpoint checks
and seem unrelated to this PR change (which only updates the temporal vs
non-temporal comparison error message).

Keeping this here for visibility — maintainer guidance appreciated if any
action is needed on my side.

[yonikremer]

I fixed the issue that causes the tests to fail, update your branch an rerun the github actions and the tests should pass

[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.51%. Comparing base (355ffac) to head (bdb544a).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
py-polars/src/polars/series/series.py	25.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25927      +/-   ##
==========================================
- Coverage   80.52%   80.51%   -0.02%     
==========================================
  Files        1764     1765       +1     
  Lines      243008   242842     -166     
  Branches     3045     3046       +1     
==========================================
- Hits       195687   195514     -173     
- Misses      46537    46543       +6     
- Partials      784      785       +1     

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[sachinn854]

All CI tests are passing now.

The Codecov warning is only from the new temporal vs non-temporal
error-message branch not being hit in tests — behavior change is minimal.

Please let me know if you'd like me to add a small unit test for coverage.