Improved docstring and added examples for Development class

[kennethshsu]

Summary of Changes

Improved doctoring documentation, added a section on the order of drop operations, and added some examples

Related GitHub Issue(s)

#704

Additional Context for Reviewers

N/A

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

---

Note

Low Risk
Documentation and doctest examples only; LDF calculation logic in fit is unchanged.

Overview
Expands Development class documentation only—no runtime or API behavior changes.

Parameter descriptions now cross-reference a new Notes (Order of Drop Operations) section that documents how drop-related options compose (n_periods → drop → drop_valuation → rank/threshold drops with preserve). average is documented as accepting literals or a list of literals. drop_high, drop_low, drop_above, and drop_below explicitly mention preserve protection.

A large Examples block adds doctest-style walkthroughs on the xyz sample triangle: inspecting link ratios, single-cell drop, per-age drop_above, combined drop_above / drop_below with preserve=3, and average="simple" for LDF output.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.18%. Comparing base (e76d85d) to head (8219602).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
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+ Coverage   86.94%   87.18%   +0.24%     
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  Files          86       86              
  Lines        4994     5143     +149     
  Branches      644      656      +12     
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+ Hits         4342     4484     +142     
- Misses        462      466       +4     
- Partials      190      193       +3     

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unittests	87.18% <ø> (+0.24%)	⬆️

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[henrydingliu]

it's difficult to appreciate these examples by examining the estimate ldf_. it would be more instructive to also show the age_to_age off the transformed triangle following this example.

ethan also has an outstanding PR that he's been working on. you'll likely have some merge conflicts.

[kennethshsu]

Let me add in the LDFs I think that's a good idea.

@EKtheSage can you respond to the PRs you submitted, I don't think you are working on the development class and my has the newer stuff that was just merged.

[henrydingliu]

i see the original ata factors, but not the transformed ata factors.

[kennethshsu]

The Development class currently doesn't return any transformed age-to-age triangle as an attribute, but it actually goes one step further and actually estimate the LDFs and CDFs.

If you think there's value is seeing the transformed age-to-age triangles we will need to implement it, but I'm not sure that should sit in the Development class because Development() is an LDF/CDF estimator. We could probably do the weights or something? This is because we want follow SKLearn's implementation where model and data are supposed to be separated.

If we want the .fit() to return another attribute called weights we can make another ticket and I can try to work on that.

[henrydingliu]

this example is for the Development class itself? so a transformed triangle should be within scope.

my original point was just that showing the ldf_ doesn't intuitively demonstrate what the drop parameter is doing. but showing the transformed link ratios does.

[kennethshsu]

That's my point. The current implantation doesn't show the transformed triangle.

Maybe I'm not following you. What code do you want to show in the docstring?

[henrydingliu]

something like cl.Development().fit_transform(tri).link_ratio. basically this.

[kennethshsu]

Ahh I see what you're saying now, that's good, I'll add that.

[henrydingliu]

how come this doesn't bring a test fail

[kennethshsu]

Ahh I got lucky, because the bottom one passes and I think it only checks the latest one (instead of appending the result).