fix: preserve RangeIndex.arange step#11328
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cfriedland5
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May 9, 2026
| transform = RangeCoordinateTransform( | ||
| start, stop, size, coord_name, dim, dtype=dtype | ||
| ) | ||
| transform._step = step |
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Assigning a different value than would be computed to a property's cache seems brittle
Replaced direct _step cache assignment with canonical stop computation, so the step property naturally produces the requested value via its own formula (stop - start) / size. Reviewer cfriedland5 correctly flagged that assigning a different value than the property would compute to a private cache field (transform._step = step) is brittle. The fix computes stop = start + size * step where size is already determined by ceil((stop - start) / step), so the step property's formula returns the requested step without touching private state. Updated the equals_exact and isel tests to match the new consistent stop behavior — arange and slicing now produce the same stop when parameters align, so exact equality holds. Co-authored-by: Claude <noreply@anthropic.com>
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Description
RangeIndex.arangecurrently computes the transform size from(stop - start) / step, but leavesRangeCoordinateTransform.stepto be derived from(stop - start) / size. Whenstepdoes not evenly divide the interval, that changes the materialized coordinate values.For example,
RangeIndex.arange(0.0, 1.0, 0.3, dim="x")currently produces coordinates spaced by0.25instead of matchingnp.arange(0.0, 1.0, 0.3).This preserves the requested
steponRangeIndex.arangetransforms and propagates the logical spacing through slice-derived transforms.Checklist
whats-new.rstapi.rstAI Disclosure
Tools: Hermes Agent / ChatGPT
Test Plan
uv run pytest xarray/tests/test_range_index.py -quv run ruff check xarray/indexes/range_index.py xarray/tests/test_range_index.pyCloses #11325