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Fix spurious invalid-value warning from Angle.to_string on some Python builds - #20618

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jdavies-st:angle-to-string-vectorize-spurious-warnings
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Fix spurious invalid-value warning from Angle.to_string on some Python builds#20618
jdavies-st wants to merge 2 commits into
astropy:mainfrom
jdavies-st:angle-to-string-vectorize-spurious-warnings

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@jdavies-st jdavies-st commented Oct 15, 2026 •
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Description

On some Python builds, Angle.to_string(), and so SkyCoord.to_string(), gives a warning even though nothing is wrong:

RuntimeWarning: invalid value encountered in do_format (vectorized)

This pull request removes that warning.

What changes for users

  • No more spurious warning. This matters most for test suites that turn warnings into errors, where it was an error. pyvo's tests, for example, fail with it if you run them with the uv-installed CPython. They don't filter for it.
  • The strings returned are exactly the same as before.
  • Masked angles still give masked strings with the same mask.

Why it happened

to_string formats each value with np.vectorize. After each call, numpy checks whether the processor recorded an "invalid value" during the calculation and, if so, warns. On the x86_64 Linux Python builds that uv installs, formatting a number can leave that record behind even though the result is fine, so numpy warns about a problem that does not exist. More detail is in #18989, astral-sh/python-build-standalone#934 and numpy/numpy#27760.

The change in this PR

  • to_string now tells numpy to ignore "invalid value" reports while it formats the values. Formatting never produces a real invalid value: NaN is handled before formatting, and on a build without this problem, main gives no warning for special values (NaN, +-inf, very large and very small numbers, +-0) and formatting options.
  • The filter in pyproject.toml that supressed this warning in astropy's tests is removed. astropy's Linux CI uses the affected astral/uv Python builds, so the existing to_string tests now fail if the warning comes back.
  • A new test checks that a masked Angle keeps its mask.

#19021 took a different approach and replaced np.vectorize with a loop. That also stopped the warning, but it had the unfortunate side effect of turning masked angles arrays into plain string arrays, formatting the masked values as if they were valid. Keeping np.vectorize avoids that, and the new test checks it.

Fixes #18989

AI Disclosure

Claude Opus 5.5 was used to help investigate, diagnose and draft the bugfix.

  • I certify that I am human and that I take full responsibility for this pull request including all interactions with reviewers.

Merge method

  • By checking this box, the PR author has requested that maintainers do NOT use the "Squash and Merge" button. Maintainers should respect this when possible; however, the final decision is at the discretion of the maintainer that merges the PR.

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Thank you for your contribution to Astropy! 🌌 This checklist is meant to remind the package maintainers who will review this pull request of some common things to look for.

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@jdavies-st
jdavies-st force-pushed the angle-to-string-vectorize-spurious-warnings branch from 92ab7c1 to 804add9 Compare October 15, 2026 15:13
@pllim pllim added this to the v7.2.3 milestone Oct 15, 2026
@pllim pllim added Bug backport-v7.2.x on-merge: backport to v7.2.x backport-v8.0.x on-merge: backport to v8.0.x labels Oct 15, 2026
neutrinoceros
neutrinoceros reviewed Oct 15, 2026
View reviewed changes
Comment thread astropy/coordinates/angles/core.py Resolved
@pllim
pllim requested a review from mhvk October 15, 2026 16:04
@astrofrog astrofrog modified the milestones: v7.2.3, v7.2.4 Oct 16, 2026
@jdavies-st
jdavies-st force-pushed the angle-to-string-vectorize-spurious-warnings branch 2 times, most recently from 5e4f36c to a6b2b0f Compare October 17, 2026 10:16
@jdavies-st
Silence the spurious invalid-value warning in Angle.to_string
4b8ce19 
- Wrap the np.vectorize call in np.errstate(invalid="ignore"). A function
  run through np.vectorize warns about floating-point flags that Python
  code leaves set, which uv's x86_64 Python builds do while formatting
- Remove the pyproject.toml filter that ignored the warning
- Add a test that a masked Angle keeps its mask
@jdavies-st
Use full URLs in code comment
fa2f577
@jdavies-st
jdavies-st force-pushed the angle-to-string-vectorize-spurious-warnings branch from a6b2b0f to fa2f577 Compare October 27, 2026 17:54
@jdavies-st

jdavies-st commented Oct 27, 2026

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@mhvk would be happy for a review on this, given you tried fixing this as well.

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Runtime error from Angle.to_string() on older python/numpy combinations

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