Fix Col.prev()/next() losing cross-frame reference, value_color() chaining, Neg type hint

[staging-devin-ai-integration]

Summary

Fixes three bugs found during code audit:

1. Col.prev() and Col.next() silently drop from_ parameter (logic bug, highest impact): When a Col is created with from_=other_frame to reference a different ExcelFrame, calling .prev(1) or .next(1) would create a new Col without passing from_ through. This caused cross-frame references to silently reference the wrong ExcelFrame, producing incorrect formulas. Introduced in commit ab6d4f0 when from_ was added to Col.

2. TableStyler.value_color() missing return self: All other fmt_* methods return Self for method chaining, but value_color() returned None, breaking chains like styler.value_color(...).fmt_number(...).

3. Neg.compute() return type annotation -> None: Should be -> Any like all other compute() methods. The function actually returns a numeric value.

Review & Testing Checklist for Human

• Verify cross-frame prev()/next() works in a real multi-table scenario (e.g., the DCF or mortgage example with cross-table references using .prev())
• Verify value_color() chaining works: styler.value_color(columns=["x"]).fmt_number(columns=["y"])
• Run pytest test/ and pyright — both pass cleanly

Notes

• All 14 tests pass (8 existing + 6 new)
• Pyright reports 0 errors
• Pre-commit hooks pass

Link to Devin session: https://staging.itsdev.in/sessions/bffcb71e53fc4b468c099a4abebd2377
Requested by: @yjhan96

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[staging-devin-ai-integration]

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[yjhan96]

Why are we adding this param here?

[staging-devin-ai-integration]

Before this fix, prev() and next() were creating a new Col without forwarding self.from_. This means if you had a cross-frame reference like:

el.col("price", from_=other_frame).prev(1)

The .prev(1) call would produce Col("price", offset=-1) — note from_ defaults to None. So instead of looking up the previous row in other_frame, it would look up the previous row in the current frame, which either references the wrong data or fails silently (e.g., if the current frame doesn't even have a "price" column).

Adding from_=self.from_ ensures the cross-frame reference is preserved through prev()/next() calls. Without from_, these methods are only correct for same-frame references.

[staging-devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.

Debug

Playground

[staging-devin-ai-integration]

Review Summary

All three fixes are correct, well-scoped, and well-tested. CI is green. LGTM — ready to merge.

Fix 1: Col.prev()/Col.next() losing from_ (highest impact)

The bug is real. get_cell_expr uses self.from_ to resolve the source frame, but prev()/next() created a new Col without forwarding it — silently reverting cross-frame references back to the current frame. The fix (from_=self.from_) is the correct one-line change in both methods.

Fix 2: TableStyler.value_color() missing return self

Confirmed: every other mutating method on TableStyler (fmt_number, fmt_currency, fmt_percent, rename_columns, etc.) returns Self for chaining. value_color() was the only outlier. Fix is straightforward.

Fix 3: Neg.compute() type hint -> None → -> Any

All 17 other compute() implementations annotate -> Any. Neg.compute() was the sole -> None, which is incorrect since it returns -value. Pyright would flag callers that rely on the return value.

Tests

The 6 new tests in test_cross_frame_ref.py provide good coverage:

• Unit tests for from_ preservation through prev()/next()
• End-to-end cross-frame formula evaluation tests (verifying computed values)
• Regression test that from_=None (same-frame) still works
• value_color() chaining test

Minor observation (not blocking)

prev()/next() don't accumulate offsets — Col("x", offset=2).prev(1) produces offset=-1, not offset=1. This is pre-existing behavior and out of scope for this PR, but worth noting for a potential follow-up if offset chaining is ever desired.

[staging-devin-ai-integration]

Closing due to inactivity for more than 7 days. Configure here.