Util weight by henrydingliu · Pull Request #940 · casact/chainladder-python

henrydingliu · 2026-06-07T23:04:35Z

Summary of Changes

Related GitHub Issue(s)

Additional Context for Reviewers

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

Note

Medium Risk
New public API and ~500 lines of weight logic that must stay consistent with Development; wrong ordering or preserve behavior would change LDFs once integrated, though production Development paths are unchanged in this diff.

Overview
Introduces TriangleWeight, a new sklearn-style utility that builds a weight triangle from the same exclusion knobs as Development (n_periods, drop, drop_valuation, drop_above/drop_below, drop_high/drop_low, preserve). It is exported from chainladder.utils and the top-level chainladder package, with EXPECTED_PUBLIC_API updated accordingly.

The implementation lives in chainladder/utils/triangle_weight.py and documents a different drop order than Development: threshold drops (drop_above/drop_below) run before rank-based drop_high/drop_low (the docstring notes steps 4 and 5 are reversed relative to Development). fit/transform set w_ on triangles and can compose with existing w_ weights.

Tests in test_development.py are expanded with _FutureDevelopment, a TriangleWeight subclass that recomputes LDFs via weighted regression, and assertions that its LDFs match Development across drop scenarios—exercising the new utility without wiring it into Development yet.

^{Reviewed by Cursor Bugbot for commit 60cabb2. Bugbot is set up for automated code reviews on this repo. Configure here.}

codecov · 2026-06-07T23:10:05Z

Codecov Report

❌ Patch coverage is 90.00000% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.53%. Comparing base (1dd5f1d) to head (60cabb2).

Files with missing lines	Patch %	Lines
chainladder/utils/triangle_weight.py	89.20%	9 Missing and 6 partials ⚠️
chainladder/development/tests/test_development.py	95.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@## #932_triangle_weight #940 +/- ##
========================================================
+ Coverage 88.30% 88.53% +0.22% 
========================================================
Files 88 89 +1 Lines 5029 5189 +160 Branches 642 658 +16 ========================================================
+ Hits 4441 4594 +153 + Misses 443 442 -1 - Partials 145 153 +8

Flag	Coverage Δ
unittests	`88.53% <90.00%> (+0.22%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

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Cursor Bugbot has reviewed your changes and found 2 potential issues.

There are 3 total unresolved issues (including 1 from previous review).

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cursor · 2026-06-08T00:36:50Z

+ if hasattr(X, "w_"):
+ self.w_ = self._set_weight_func(
+ X=X * X.w_,
+ )


Prior weights use wrong attribute
Medium Severity
When prior weights exist, TriangleWeight.fit multiplies the input triangle by X.w_ and passes that triangle into _set_weight_func. Development.fit instead checks w_v2_ and combines prior weights on obj.age_to_age. After Development, w_ and w_v2_ can differ, so chained weighting no longer matches development’s v2 path.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ else:
+ self.w_ = self._set_weight_func(
+ X=X,
+ )


Ratio drops need age-to-age
Medium Severity
TriangleWeight.fit feeds the caller’s triangle straight into _set_weight_func, so _drop_x_func and _drop_n_func rank and threshold X.values as given. Those steps expect age-to-age link ratios; Development always builds v2 weights from obj.age_to_age. The same cumulative triangle passed to Development.fit can get incorrect exclusions here.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

henrydingliu · 2026-06-07T23:04:35Z

Summary of Changes

Related GitHub Issue(s)

Additional Context for Reviewers

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

Note

Medium Risk
New public API and ~500 lines of weight logic that must stay consistent with Development; wrong ordering or preserve behavior would change LDFs once integrated, though production Development paths are unchanged in this diff.

Overview
Introduces TriangleWeight, a new sklearn-style utility that builds a weight triangle from the same exclusion knobs as Development (n_periods, drop, drop_valuation, drop_above/drop_below, drop_high/drop_low, preserve). It is exported from chainladder.utils and the top-level chainladder package, with EXPECTED_PUBLIC_API updated accordingly.

The implementation lives in chainladder/utils/triangle_weight.py and documents a different drop order than Development: threshold drops (drop_above/drop_below) run before rank-based drop_high/drop_low (the docstring notes steps 4 and 5 are reversed relative to Development). fit/transform set w_ on triangles and can compose with existing w_ weights.

Tests in test_development.py are expanded with _FutureDevelopment, a TriangleWeight subclass that recomputes LDFs via weighted regression, and assertions that its LDFs match Development across drop scenarios—exercising the new utility without wiring it into Development yet.

^{Reviewed by Cursor Bugbot for commit 60cabb2. Bugbot is set up for automated code reviews on this repo. Configure here.}

codecov · 2026-06-07T23:10:05Z

Codecov Report

❌ Patch coverage is 90.00000% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.53%. Comparing base (1dd5f1d) to head (60cabb2).

Files with missing lines	Patch %	Lines
chainladder/utils/triangle_weight.py	89.20%	9 Missing and 6 partials ⚠️
chainladder/development/tests/test_development.py	95.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@## #932_triangle_weight #940 +/- ##
========================================================
+ Coverage 88.30% 88.53% +0.22% 
========================================================
Files 88 89 +1 Lines 5029 5189 +160 Branches 642 658 +16 ========================================================
+ Hits 4441 4594 +153 + Misses 443 442 -1 - Partials 145 153 +8

Flag	Coverage Δ
unittests	`88.53% <90.00%> (+0.22%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
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cursor

Cursor Bugbot has reviewed your changes and found 2 potential issues.

There are 3 total unresolved issues (including 1 from previous review).

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ if hasattr(X, "w_"):
+ self.w_ = self._set_weight_func(
+ X=X * X.w_,
+ )


Prior weights use wrong attribute
Medium Severity
When prior weights exist, TriangleWeight.fit multiplies the input triangle by X.w_ and passes that triangle into _set_weight_func. Development.fit instead checks w_v2_ and combines prior weights on obj.age_to_age. After Development, w_ and w_v2_ can differ, so chained weighting no longer matches development’s v2 path.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ else:
+ self.w_ = self._set_weight_func(
+ X=X,
+ )


Ratio drops need age-to-age
Medium Severity
TriangleWeight.fit feeds the caller’s triangle straight into _set_weight_func, so _drop_x_func and _drop_n_func rank and threshold X.values as given. Those steps expect age-to-age link ratios; Development always builds v2 weights from obj.age_to_age. The same cumulative triangle passed to Development.fit can get incorrect exclusions here.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

henrydingliu · 2026-06-07T23:04:35Z

Summary of Changes

Related GitHub Issue(s)

Additional Context for Reviewers

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

Note

Medium Risk
New public API and ~500 lines of weight logic that must stay consistent with Development; wrong ordering or preserve behavior would change LDFs once integrated, though production Development paths are unchanged in this diff.

Overview
Introduces TriangleWeight, a new sklearn-style utility that builds a weight triangle from the same exclusion knobs as Development (n_periods, drop, drop_valuation, drop_above/drop_below, drop_high/drop_low, preserve). It is exported from chainladder.utils and the top-level chainladder package, with EXPECTED_PUBLIC_API updated accordingly.

The implementation lives in chainladder/utils/triangle_weight.py and documents a different drop order than Development: threshold drops (drop_above/drop_below) run before rank-based drop_high/drop_low (the docstring notes steps 4 and 5 are reversed relative to Development). fit/transform set w_ on triangles and can compose with existing w_ weights.

Tests in test_development.py are expanded with _FutureDevelopment, a TriangleWeight subclass that recomputes LDFs via weighted regression, and assertions that its LDFs match Development across drop scenarios—exercising the new utility without wiring it into Development yet.

^{Reviewed by Cursor Bugbot for commit 60cabb2. Bugbot is set up for automated code reviews on this repo. Configure here.}

codecov · 2026-06-07T23:10:05Z

Codecov Report

❌ Patch coverage is 90.00000% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.53%. Comparing base (1dd5f1d) to head (60cabb2).

Files with missing lines	Patch %	Lines
chainladder/utils/triangle_weight.py	89.20%	9 Missing and 6 partials ⚠️
chainladder/development/tests/test_development.py	95.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@## #932_triangle_weight #940 +/- ##
========================================================
+ Coverage 88.30% 88.53% +0.22% 
========================================================
Files 88 89 +1 Lines 5029 5189 +160 Branches 642 658 +16 ========================================================
+ Hits 4441 4594 +153 + Misses 443 442 -1 - Partials 145 153 +8

Flag	Coverage Δ
unittests	`88.53% <90.00%> (+0.22%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

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cursor

Cursor Bugbot has reviewed your changes and found 2 potential issues.

There are 3 total unresolved issues (including 1 from previous review).

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ if hasattr(X, "w_"):
+ self.w_ = self._set_weight_func(
+ X=X * X.w_,
+ )


Prior weights use wrong attribute
Medium Severity
When prior weights exist, TriangleWeight.fit multiplies the input triangle by X.w_ and passes that triangle into _set_weight_func. Development.fit instead checks w_v2_ and combines prior weights on obj.age_to_age. After Development, w_ and w_v2_ can differ, so chained weighting no longer matches development’s v2 path.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ else:
+ self.w_ = self._set_weight_func(
+ X=X,
+ )


Ratio drops need age-to-age
Medium Severity
TriangleWeight.fit feeds the caller’s triangle straight into _set_weight_func, so _drop_x_func and _drop_n_func rank and threshold X.values as given. Those steps expect age-to-age link ratios; Development always builds v2 weights from obj.age_to_age. The same cumulative triangle passed to Development.fit can get incorrect exclusions here.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

henrydingliu · 2026-06-07T23:04:35Z

Summary of Changes

Related GitHub Issue(s)

Additional Context for Reviewers

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

Note

Medium Risk
New public API and ~500 lines of weight logic that must stay consistent with Development; wrong ordering or preserve behavior would change LDFs once integrated, though production Development paths are unchanged in this diff.

Overview
Introduces TriangleWeight, a new sklearn-style utility that builds a weight triangle from the same exclusion knobs as Development (n_periods, drop, drop_valuation, drop_above/drop_below, drop_high/drop_low, preserve). It is exported from chainladder.utils and the top-level chainladder package, with EXPECTED_PUBLIC_API updated accordingly.

The implementation lives in chainladder/utils/triangle_weight.py and documents a different drop order than Development: threshold drops (drop_above/drop_below) run before rank-based drop_high/drop_low (the docstring notes steps 4 and 5 are reversed relative to Development). fit/transform set w_ on triangles and can compose with existing w_ weights.

Tests in test_development.py are expanded with _FutureDevelopment, a TriangleWeight subclass that recomputes LDFs via weighted regression, and assertions that its LDFs match Development across drop scenarios—exercising the new utility without wiring it into Development yet.

^{Reviewed by Cursor Bugbot for commit 60cabb2. Bugbot is set up for automated code reviews on this repo. Configure here.}

codecov · 2026-06-07T23:10:05Z

Codecov Report

❌ Patch coverage is 90.00000% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.53%. Comparing base (1dd5f1d) to head (60cabb2).

Files with missing lines	Patch %	Lines
chainladder/utils/triangle_weight.py	89.20%	9 Missing and 6 partials ⚠️
chainladder/development/tests/test_development.py	95.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@## #932_triangle_weight #940 +/- ##
========================================================
+ Coverage 88.30% 88.53% +0.22% 
========================================================
Files 88 89 +1 Lines 5029 5189 +160 Branches 642 658 +16 ========================================================
+ Hits 4441 4594 +153 + Misses 443 442 -1 - Partials 145 153 +8

Flag	Coverage Δ
unittests	`88.53% <90.00%> (+0.22%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

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cursor

Cursor Bugbot has reviewed your changes and found 2 potential issues.

There are 3 total unresolved issues (including 1 from previous review).

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ if hasattr(X, "w_"):
+ self.w_ = self._set_weight_func(
+ X=X * X.w_,
+ )


Prior weights use wrong attribute
Medium Severity
When prior weights exist, TriangleWeight.fit multiplies the input triangle by X.w_ and passes that triangle into _set_weight_func. Development.fit instead checks w_v2_ and combines prior weights on obj.age_to_age. After Development, w_ and w_v2_ can differ, so chained weighting no longer matches development’s v2 path.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ else:
+ self.w_ = self._set_weight_func(
+ X=X,
+ )


Ratio drops need age-to-age
Medium Severity
TriangleWeight.fit feeds the caller’s triangle straight into _set_weight_func, so _drop_x_func and _drop_n_func rank and threshold X.values as given. Those steps expect age-to-age link ratios; Development always builds v2 weights from obj.age_to_age. The same cumulative triangle passed to Development.fit can get incorrect exclusions here.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

henrydingliu · 2026-06-07T23:04:35Z

Summary of Changes

Related GitHub Issue(s)

Additional Context for Reviewers

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

Note

Medium Risk
New public API and ~500 lines of weight logic that must stay consistent with Development; wrong ordering or preserve behavior would change LDFs once integrated, though production Development paths are unchanged in this diff.

Overview
Introduces TriangleWeight, a new sklearn-style utility that builds a weight triangle from the same exclusion knobs as Development (n_periods, drop, drop_valuation, drop_above/drop_below, drop_high/drop_low, preserve). It is exported from chainladder.utils and the top-level chainladder package, with EXPECTED_PUBLIC_API updated accordingly.

The implementation lives in chainladder/utils/triangle_weight.py and documents a different drop order than Development: threshold drops (drop_above/drop_below) run before rank-based drop_high/drop_low (the docstring notes steps 4 and 5 are reversed relative to Development). fit/transform set w_ on triangles and can compose with existing w_ weights.

Tests in test_development.py are expanded with _FutureDevelopment, a TriangleWeight subclass that recomputes LDFs via weighted regression, and assertions that its LDFs match Development across drop scenarios—exercising the new utility without wiring it into Development yet.

^{Reviewed by Cursor Bugbot for commit 60cabb2. Bugbot is set up for automated code reviews on this repo. Configure here.}

codecov · 2026-06-07T23:10:05Z

Codecov Report

❌ Patch coverage is 90.00000% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.53%. Comparing base (1dd5f1d) to head (60cabb2).

Files with missing lines	Patch %	Lines
chainladder/utils/triangle_weight.py	89.20%	9 Missing and 6 partials ⚠️
chainladder/development/tests/test_development.py	95.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@## #932_triangle_weight #940 +/- ##
========================================================
+ Coverage 88.30% 88.53% +0.22% 
========================================================
Files 88 89 +1 Lines 5029 5189 +160 Branches 642 658 +16 ========================================================
+ Hits 4441 4594 +153 + Misses 443 442 -1 - Partials 145 153 +8

Flag	Coverage Δ
unittests	`88.53% <90.00%> (+0.22%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

cursor

Cursor Bugbot has reviewed your changes and found 2 potential issues.

There are 3 total unresolved issues (including 1 from previous review).

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ if hasattr(X, "w_"):
+ self.w_ = self._set_weight_func(
+ X=X * X.w_,
+ )


Prior weights use wrong attribute
Medium Severity
When prior weights exist, TriangleWeight.fit multiplies the input triangle by X.w_ and passes that triangle into _set_weight_func. Development.fit instead checks w_v2_ and combines prior weights on obj.age_to_age. After Development, w_ and w_v2_ can differ, so chained weighting no longer matches development’s v2 path.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ else:
+ self.w_ = self._set_weight_func(
+ X=X,
+ )


Ratio drops need age-to-age
Medium Severity
TriangleWeight.fit feeds the caller’s triangle straight into _set_weight_func, so _drop_x_func and _drop_n_func rank and threshold X.values as given. Those steps expect age-to-age link ratios; Development always builds v2 weights from obj.age_to_age. The same cumulative triangle passed to Development.fit can get incorrect exclusions here.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

henrydingliu · 2026-06-07T23:04:35Z

Summary of Changes

Related GitHub Issue(s)

Additional Context for Reviewers

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

Note

Medium Risk
New public API and ~500 lines of weight logic that must stay consistent with Development; wrong ordering or preserve behavior would change LDFs once integrated, though production Development paths are unchanged in this diff.

Overview
Introduces TriangleWeight, a new sklearn-style utility that builds a weight triangle from the same exclusion knobs as Development (n_periods, drop, drop_valuation, drop_above/drop_below, drop_high/drop_low, preserve). It is exported from chainladder.utils and the top-level chainladder package, with EXPECTED_PUBLIC_API updated accordingly.

The implementation lives in chainladder/utils/triangle_weight.py and documents a different drop order than Development: threshold drops (drop_above/drop_below) run before rank-based drop_high/drop_low (the docstring notes steps 4 and 5 are reversed relative to Development). fit/transform set w_ on triangles and can compose with existing w_ weights.

Tests in test_development.py are expanded with _FutureDevelopment, a TriangleWeight subclass that recomputes LDFs via weighted regression, and assertions that its LDFs match Development across drop scenarios—exercising the new utility without wiring it into Development yet.

^{Reviewed by Cursor Bugbot for commit 60cabb2. Bugbot is set up for automated code reviews on this repo. Configure here.}

codecov · 2026-06-07T23:10:05Z

Codecov Report

❌ Patch coverage is 90.00000% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.53%. Comparing base (1dd5f1d) to head (60cabb2).

Files with missing lines	Patch %	Lines
chainladder/utils/triangle_weight.py	89.20%	9 Missing and 6 partials ⚠️
chainladder/development/tests/test_development.py	95.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@## #932_triangle_weight #940 +/- ##
========================================================
+ Coverage 88.30% 88.53% +0.22% 
========================================================
Files 88 89 +1 Lines 5029 5189 +160 Branches 642 658 +16 ========================================================
+ Hits 4441 4594 +153 + Misses 443 442 -1 - Partials 145 153 +8

Flag	Coverage Δ
unittests	`88.53% <90.00%> (+0.22%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

cursor

Cursor Bugbot has reviewed your changes and found 2 potential issues.

There are 3 total unresolved issues (including 1 from previous review).

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ if hasattr(X, "w_"):
+ self.w_ = self._set_weight_func(
+ X=X * X.w_,
+ )


Prior weights use wrong attribute
Medium Severity
When prior weights exist, TriangleWeight.fit multiplies the input triangle by X.w_ and passes that triangle into _set_weight_func. Development.fit instead checks w_v2_ and combines prior weights on obj.age_to_age. After Development, w_ and w_v2_ can differ, so chained weighting no longer matches development’s v2 path.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ else:
+ self.w_ = self._set_weight_func(
+ X=X,
+ )


Ratio drops need age-to-age
Medium Severity
TriangleWeight.fit feeds the caller’s triangle straight into _set_weight_func, so _drop_x_func and _drop_n_func rank and threshold X.values as given. Those steps expect age-to-age link ratios; Development always builds v2 weights from obj.age_to_age. The same cumulative triangle passed to Development.fit can get incorrect exclusions here.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

henrydingliu · 2026-06-07T23:04:35Z

Summary of Changes

Related GitHub Issue(s)

Additional Context for Reviewers

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

Note

Medium Risk
New public API and ~500 lines of weight logic that must stay consistent with Development; wrong ordering or preserve behavior would change LDFs once integrated, though production Development paths are unchanged in this diff.

Overview
Introduces TriangleWeight, a new sklearn-style utility that builds a weight triangle from the same exclusion knobs as Development (n_periods, drop, drop_valuation, drop_above/drop_below, drop_high/drop_low, preserve). It is exported from chainladder.utils and the top-level chainladder package, with EXPECTED_PUBLIC_API updated accordingly.

The implementation lives in chainladder/utils/triangle_weight.py and documents a different drop order than Development: threshold drops (drop_above/drop_below) run before rank-based drop_high/drop_low (the docstring notes steps 4 and 5 are reversed relative to Development). fit/transform set w_ on triangles and can compose with existing w_ weights.

Tests in test_development.py are expanded with _FutureDevelopment, a TriangleWeight subclass that recomputes LDFs via weighted regression, and assertions that its LDFs match Development across drop scenarios—exercising the new utility without wiring it into Development yet.

^{Reviewed by Cursor Bugbot for commit 60cabb2. Bugbot is set up for automated code reviews on this repo. Configure here.}

codecov · 2026-06-07T23:10:05Z

Codecov Report

❌ Patch coverage is 90.00000% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.53%. Comparing base (1dd5f1d) to head (60cabb2).

Files with missing lines	Patch %	Lines
chainladder/utils/triangle_weight.py	89.20%	9 Missing and 6 partials ⚠️
chainladder/development/tests/test_development.py	95.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@## #932_triangle_weight #940 +/- ##
========================================================
+ Coverage 88.30% 88.53% +0.22% 
========================================================
Files 88 89 +1 Lines 5029 5189 +160 Branches 642 658 +16 ========================================================
+ Hits 4441 4594 +153 + Misses 443 442 -1 - Partials 145 153 +8

Flag	Coverage Δ
unittests	`88.53% <90.00%> (+0.22%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

cursor

Cursor Bugbot has reviewed your changes and found 2 potential issues.

There are 3 total unresolved issues (including 1 from previous review).

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ if hasattr(X, "w_"):
+ self.w_ = self._set_weight_func(
+ X=X * X.w_,
+ )


Prior weights use wrong attribute
Medium Severity
When prior weights exist, TriangleWeight.fit multiplies the input triangle by X.w_ and passes that triangle into _set_weight_func. Development.fit instead checks w_v2_ and combines prior weights on obj.age_to_age. After Development, w_ and w_v2_ can differ, so chained weighting no longer matches development’s v2 path.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ else:
+ self.w_ = self._set_weight_func(
+ X=X,
+ )


Ratio drops need age-to-age
Medium Severity
TriangleWeight.fit feeds the caller’s triangle straight into _set_weight_func, so _drop_x_func and _drop_n_func rank and threshold X.values as given. Those steps expect age-to-age link ratios; Development always builds v2 weights from obj.age_to_age. The same cumulative triangle passed to Development.fit can get incorrect exclusions here.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

henrydingliu · 2026-06-07T23:04:35Z

Summary of Changes

Related GitHub Issue(s)

Additional Context for Reviewers

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

Note

Medium Risk
New public API and ~500 lines of weight logic that must stay consistent with Development; wrong ordering or preserve behavior would change LDFs once integrated, though production Development paths are unchanged in this diff.

Overview
Introduces TriangleWeight, a new sklearn-style utility that builds a weight triangle from the same exclusion knobs as Development (n_periods, drop, drop_valuation, drop_above/drop_below, drop_high/drop_low, preserve). It is exported from chainladder.utils and the top-level chainladder package, with EXPECTED_PUBLIC_API updated accordingly.

The implementation lives in chainladder/utils/triangle_weight.py and documents a different drop order than Development: threshold drops (drop_above/drop_below) run before rank-based drop_high/drop_low (the docstring notes steps 4 and 5 are reversed relative to Development). fit/transform set w_ on triangles and can compose with existing w_ weights.

Tests in test_development.py are expanded with _FutureDevelopment, a TriangleWeight subclass that recomputes LDFs via weighted regression, and assertions that its LDFs match Development across drop scenarios—exercising the new utility without wiring it into Development yet.

^{Reviewed by Cursor Bugbot for commit 60cabb2. Bugbot is set up for automated code reviews on this repo. Configure here.}

codecov · 2026-06-07T23:10:05Z

Codecov Report

❌ Patch coverage is 90.00000% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.53%. Comparing base (1dd5f1d) to head (60cabb2).

Files with missing lines	Patch %	Lines
chainladder/utils/triangle_weight.py	89.20%	9 Missing and 6 partials ⚠️
chainladder/development/tests/test_development.py	95.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@ Coverage Diff @@## #932_triangle_weight #940 +/- ##
========================================================
+ Coverage 88.30% 88.53% +0.22% 
========================================================
Files 88 89 +1 Lines 5029 5189 +160 Branches 642 658 +16 ========================================================
+ Hits 4441 4594 +153 + Misses 443 442 -1 - Partials 145 153 +8

Flag	Coverage Δ
unittests	`88.53% <90.00%> (+0.22%)`	⬆️

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cursor

Cursor Bugbot has reviewed your changes and found 2 potential issues.

There are 3 total unresolved issues (including 1 from previous review).

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ if hasattr(X, "w_"):
+ self.w_ = self._set_weight_func(
+ X=X * X.w_,
+ )


Prior weights use wrong attribute
Medium Severity
When prior weights exist, TriangleWeight.fit multiplies the input triangle by X.w_ and passes that triangle into _set_weight_func. Development.fit instead checks w_v2_ and combines prior weights on obj.age_to_age. After Development, w_ and w_v2_ can differ, so chained weighting no longer matches development’s v2 path.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

cursor · 2026-06-08T00:36:50Z

+ else:
+ self.w_ = self._set_weight_func(
+ X=X,
+ )


Ratio drops need age-to-age
Medium Severity
TriangleWeight.fit feeds the caller’s triangle straight into _set_weight_func, so _drop_x_func and _drop_n_func rank and threshold X.values as given. Those steps expect age-to-age link ratios; Development always builds v2 weights from obj.age_to_age. The same cumulative triangle passed to Development.fit can get incorrect exclusions here.
^{Reviewed by Cursor Bugbot for commit ca2f50d. Configure here.}

henrydingliu added 2 commits June 7, 2026 22:30

adding triangle_weight
bb523d0

fixing test
e2fc3c8

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more test fixes
8d62bd8

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adding type hinting
ca2f50d

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editing docstring to reflect implementation
60cabb2

henrydingliu marked this pull request as ready for review June 8, 2026 01:01

henrydingliu requested review from genedan, jbogaardt and kennethshsu as code owners June 8, 2026 01:01

henrydingliu merged commit 9a9a796 into casact:#932_triangle_weightJun 8, 2026
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adding triangle_weight
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fixing test
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more test fixes
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adding type hinting
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editing docstring to reflect implementation
60cabb2

henrydingliu marked this pull request as ready for review June 8, 2026 01:01

henrydingliu requested review from genedan, jbogaardt and kennethshsu as code owners June 8, 2026 01:01

henrydingliu merged commit 9a9a796 into casact:#932_triangle_weightJun 8, 2026
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adding triangle_weight
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fixing test
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more test fixes
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adding type hinting
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editing docstring to reflect implementation
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henrydingliu marked this pull request as ready for review June 8, 2026 01:01

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henrydingliu merged commit 9a9a796 into casact:#932_triangle_weightJun 8, 2026
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adding triangle_weight
bb523d0

fixing test
e2fc3c8

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more test fixes
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adding type hinting
ca2f50d

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editing docstring to reflect implementation
60cabb2

henrydingliu marked this pull request as ready for review June 8, 2026 01:01

henrydingliu requested review from genedan, jbogaardt and kennethshsu as code owners June 8, 2026 01:01

henrydingliu merged commit 9a9a796 into casact:#932_triangle_weightJun 8, 2026
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adding triangle_weight
bb523d0

fixing test
e2fc3c8

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Comment threadchainladder/development/tests/test_development.py Outdated

more test fixes
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adding type hinting
ca2f50d

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editing docstring to reflect implementation
60cabb2

henrydingliu marked this pull request as ready for review June 8, 2026 01:01

henrydingliu requested review from genedan, jbogaardt and kennethshsu as code owners June 8, 2026 01:01

henrydingliu merged commit 9a9a796 into casact:#932_triangle_weightJun 8, 2026
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henrydingliu added 2 commits June 7, 2026 22:30

adding triangle_weight
bb523d0

fixing test
e2fc3c8

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Comment threadchainladder/development/tests/test_development.py Outdated

more test fixes
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adding type hinting
ca2f50d

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editing docstring to reflect implementation
60cabb2

henrydingliu marked this pull request as ready for review June 8, 2026 01:01

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henrydingliu merged commit 9a9a796 into casact:#932_triangle_weightJun 8, 2026
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adding triangle_weight
bb523d0

fixing test
e2fc3c8

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more test fixes
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adding type hinting
ca2f50d

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editing docstring to reflect implementation
60cabb2

henrydingliu marked this pull request as ready for review June 8, 2026 01:01

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henrydingliu merged commit 9a9a796 into casact:#932_triangle_weightJun 8, 2026
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adding triangle_weight
bb523d0

fixing test
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more test fixes
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adding type hinting
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editing docstring to reflect implementation
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henrydingliu marked this pull request as ready for review June 8, 2026 01:01

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