feat(core): allow Triangle.drop() development dropping, label validation, and error options

[priyam0k]

Summary of Changes

• completes Triangle.drop() functionality for Add parameters to Triangle.drop() #1052:

  • drop development periods via development=, axis=3, or axis='development'. requires dropping first/last periods to prevent gaps.
  • validates labels=None. raises ValueError if no labels or axis keywords are passed.
  • adds level and errors parameters (errors='ignore' suppresses missing label KeyErrors).

• Resolved all Ruff lint violations in pandas.py and test_triangle.py and removed both files from ignore in pyproject.toml (part of Initial Linting Cleanup #1216).

Related GitHub Issue(s)

closes #1057 #1062 #1061
part of #1052
part of #1216

Additional Context for Reviewers

• Allow TrianglePandas.drop() to drop index labels #1051 (index label dropping) remains
• all core logic changes for Triangle.drop() are in chainladder/core/pandas.py (and the new drop unit tests in test_triangle.py).
• the extra ruff edits in pandas.py (2 minor lints) and test_triangle.py (legacy boolean equality lints) were required for pre-commit CI to pass. all bugbot findings are also fully resolved.

Checklist

• I passed tests locally for both code (uv run pytest) and documentation changes (uv run --directory docs jb build . --builder=custom --custom-builder=doctest)

---

Note

Medium Risk
Changes core Triangle slicing/drop semantics on origin and development axes and valuation metadata; behavior is well covered by new tests but affects user-facing data shape logic.

Overview
Triangle.drop() now supports dropping development periods via development=, axis=3, or axis='development', with the same first/last-only rule as origin (interior drops raise ValueError). Missing labels honor a new errors parameter ('raise' vs 'ignore'); level is accepted for API parity but only allowed with the index axis (still unimplemented).

Input validation is tighter: calling drop() with no labels/axis keywords raises ValueError, and columns/origin/development missing-label checks respect errors. After development drops on valuation triangles, valuation_date is updated; dropping the ultimate dev period clears is_ultimate. Origin-drop dev trimming after NaN columns now uses NumPy dense paths instead of the backend array module.

Docs/examples cover development dropping; hvplot uses isinstance for PeriodIndex. Ruff cleanups in pandas.py and test_triangle.py plus removal of those files from pyproject.toml per-file ignores; extensive new unit tests cover drop behavior.

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[github-actions]

Pyright Type Completeness

View the full pyright --verifytypes output for this commit

Project (full chainladder package, at this PR's head): 14.9% of exported symbols fully typed (202 / 1355)

	Known	Ambiguous	Unknown	Total
Project (head)	202	111	1042	1355

Other symbols referenced but not exported by chainladder: 13

	Known	Ambiguous	Unknown	Total
Other (head)	3	1	9	13

Symbols without documentation:

• Functions without docstring: 323
• Functions without default param: 0
• Classes without docstring: 10

Patch (exported symbols added or changed by this PR): 0.0% fully typed (0 / 20); 1 no longer exported

	Known	Ambiguous	Unknown	Total
Patch	0	0	20	20

Patch symbol details

Symbol	Status	Change
chainladder.core.tests.test_triangle.test_drop_both_labels_and_alternative_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_both_labels_and_axis_keyword_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_development_axis_equivalents	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_development_first	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_development_interior_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_development_last	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_development_missing_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_development_updates_valuation_date	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_errors_ignore	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_index_alternative_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_index_axis_not_implemented_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_interior_development_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_interior_origin_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_invalid_errors_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_level_non_index_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_no_arguments_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_no_labels_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_ultimate_column_updates_is_ultimate	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_unsupported_axis_raises	❌ unknown	new
chainladder.core.tests.test_triangle.test_hvplot_passthrough	❌ unknown	new
chainladder.core.tests.test_triangle.test_drop_index_origin_development_alternatives_raise	—	no longer exported (was ❌ unknown)

[codecov]

Codecov Report

❌ Patch coverage is 90.32258% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.31%. Comparing base (606be5c) to head (8d05187).

Files with missing lines	Patch %	Lines
chainladder/core/pandas.py	90.32%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1207      +/-   ##
==========================================
+ Coverage   91.27%   91.31%   +0.03%     
==========================================
  Files          91       91              
  Lines        5411     5434      +23     
  Branches      692      700       +8     
==========================================
+ Hits         4939     4962      +23     
+ Misses        338      336       -2     
- Partials      134      136       +2     

Flag	Coverage Δ
unittests	91.31% <90.32%> (+0.03%)	⬆️

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[henrydingliu]

these reviews are gonna be challenging, with the mix of ruff debugging and actual code change.

@genedan would love to get your take

[priyam0k]

all core logic changes for Triangle.drop() are in chainladder/core/pandas.py (and the new drop unit tests in test_triangle.py).

the extra ruff edits in pandas.py (2 minor lints) and test_triangle.py (legacy boolean equality lints) were required for pre-commit CI to pass. all bugbot findings are also fully resolved.

[henrydingliu]

need to cover one more line to meet patch coverage

[henrydingliu]

friendly reminder to edit pyproject after you fix the ruff violations

[priyam0k]

thanks removed per-file-ignores in pyproject.toml , (part of #1216)

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[priyam0k]

@henrydingliu all CI checks and tests are passing. updated pyproject.toml as requested.
codecov patch runs early before all test matrix runners finish uploading, can open an issue to fix codecov.yml if needed. ready for review!

[henrydingliu]

looking at the time stamps, codecov patch starts after unittest is done. the same new lines for checking missing columns show as uncovered in both patch and project. in any case, 90% diff hit is sufficient for merging. i can approve once conflict is resolved.