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Fix crash on prime after single-character superscript - #32066

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tacaswell merged 1 commit into
matplotlib:mainfrom
jameslin9968:fix-mathtext-single-char-superscript-prime
Jul 18, 2026
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Fix crash on prime after single-character superscript#32066
tacaswell merged 1 commit into
matplotlib:mainfrom
jameslin9968:fix-mathtext-single-char-superscript-prime

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@jameslin9968

@jameslin9968 jameslin9968 commented Jul 18, 2026 •
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A prime (apostrophe) following a single-character superscript such as $x^2'$ raised AttributeError: 'Char' object has no attribute 'children'. A single-character superscript is parsed as a bare Char, whereas the apostrophe handling in Parser.subsuper assumed the superscript was an Hlist and called super.children.extend(...). The braced form $x^{2}'$ already produced an Hlist and worked.

The fix wraps a non-Hlist superscript in an Hlist before appending the prime glyphs, matching the braced case.

PR summary

Minimal reproduction (crashes on current main / released matplotlib):

import matplotlib.pyplot as plt
fig = plt.figure()
fig.text(0.1, 0.5, r"$x^2'$")   # prime after single-char superscript
fig.savefig("out.png")          # -> AttributeError: 'Char' object has no attribute 'children'

With this PR the expression renders correctly, matching the already-working braced form $x^{2}'$.

AI Disclosure

This PR was authored with substantial AI assistance (Claude). AI was used to localize the bug in Parser.subsuper, write the fix, and generate the parametrized regression tests in test_mathtext.py. All changes were run and verified locally: the new tests fail without the fix and pass with it, and the full test_mathtext.py suite passes (732 passed / 0 failed).

PR checklist

  • [N/A] "closes #0000" — no pre-existing issue was filed for this crash
  • new and changed code is tested (4 parametrized cases in test_mathtext.py)
  • [N/A] Plotting related features are demonstrated in an example — bugfix, no new feature
  • [N/A] New Features and API Changes are noted in a release note — behavior-only bugfix, none needed
  • Documentation complies with guidelines — no doc changes needed

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@tacaswell tacaswell added this to the v3.11.2 milestone Jul 18, 2026
@scottshambaugh

scottshambaugh commented Jul 18, 2026

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Please fill out the rest of the PR checklist (I see Claude coauthorship but no AI disclosure) and provide a minimal script that demonstrates the issue.

@scottshambaugh scottshambaugh added ai-contribution PRs that are AI generated without a human in the loop status: autoclose candidate PRs that are not yet ready for review and may be automatically closed in two weeks labels Jul 18, 2026
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@tacaswell

tacaswell commented Jul 18, 2026

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Please don't make an issue, the PR is enough.

@jameslin9968 is at the SciPy sprints with us.

@tacaswell

tacaswell commented Jul 18, 2026

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from matplotlib import pyplot as plt
fig, ax = plt.subplots()

for j, t in enumerate([r"$x^{2}'$", r"$x^{a}'$", r"$x^{2}''$", r"$x^{\alpha}'$"]):
    ax.text(j, .5, t)


fig, ax = plt.subplots()

for j, t in enumerate([r"$x^2'$", r"$x^a'$", r"$x^2''$", r"$x^\alpha'$"]):
    ax.text(j, .5, t)

@scottshambaugh scottshambaugh removed ai-contribution PRs that are AI generated without a human in the loop status: autoclose candidate PRs that are not yet ready for review and may be automatically closed in two weeks labels Jul 18, 2026
@jameslin9968

jameslin9968 commented Jul 18, 2026

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Thanks for the review, @scottshambaugh. I've updated the PR description:

  • Filled in the PR checklist.
  • Added an AI Disclosure section — this PR was authored with substantial AI (Claude) assistance, and all changes were verified locally (new tests fail without the fix, pass with it; full test_mathtext.py passes, 732 passed / 0 failed).
  • Added a minimal reproduction script that crashes on current main and released matplotlib.

No pre-existing issue was filed for this crash, so the checklist's "closes #" is marked N/A. Happy to open one if you'd prefer it tracked separately.

@scottshambaugh

scottshambaugh commented Jul 18, 2026 •
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I cannot reproduce this locally on main, what OS / backend is this using?

Edit: Got it reproducing locally.

scottshambaugh
scottshambaugh approved these changes Jul 18, 2026
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My preference would be for the new comments to be trimmed way down, but this looks good to me otherwise.

@jameslin9968 @claude
Fix crash on prime after single-character superscript
720a33e 
A prime (apostrophe) following a single-character superscript such as
``$x^2'$`` raised ``AttributeError: 'Char' object has no attribute
'children'``. A single-character superscript is parsed as a bare ``Char``,
whereas the apostrophe handling in ``Parser.subsuper`` assumed the
superscript was an ``Hlist`` and called ``super.children.extend(...)``.
The braced form ``$x^{2}'$`` already produced an ``Hlist`` and worked.

Wrap a non-``Hlist`` superscript in an ``Hlist`` before appending the
prime glyphs, matching the braced case.

Co-Authored-By: Claude Opus 4.8 <[email protected]>
@jameslin9968
jameslin9968 force-pushed the fix-mathtext-single-char-superscript-prime branch from 0986c14 to 720a33e Compare July 18, 2026 20:21
@jameslin9968

jameslin9968 commented Jul 18, 2026

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Thanks @scottshambaugh, @tacaswell. Trimmed the comments in both the fix and the test down to one line each. Force-pushed.

@tacaswell
tacaswell merged commit 9ad800b into matplotlib:main Jul 18, 2026
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@meeseeksmachine meeseeksmachine mentioned this pull request Jul 18, 2026
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@tacaswell

tacaswell commented Jul 18, 2026

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Thank you @jameslin9968 and it was great to talk to you at the sprints today. I hope we hear from you agian!

timhoffm pushed a commit that referenced this pull request Jul 19, 2026
@tacaswell @meeseeksmachine
Backport PR #32066: Fix crash on prime after single-character supersc…
8e01118 
…ript
timhoffm added a commit that referenced this pull request Jul 19, 2026
@timhoffm
Merge pull request #32070 from meeseeksmachine/auto-backport-of-pr-32…
f5ccc77 
…066-on-v3.11.x

Backport PR #32066 on branch v3.11.x (Fix crash on prime after single-character superscript)
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