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GeezerVison is showing github.com — gh-125788: Improve ctypes error message for mismatched callback prototypes by aribaskagan · Pull Request #161873 · python/cpython

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@aribaskagan

@aribaskagan aribaskagan commented Nov 12, 2026 •
edited by bedevere-app Bot
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When a CFUNCTYPE/WINFUNCTYPE callback is passed where a different callback prototype is expected, ctypes raised a confusing error because both prototype classes share the name CFunctionType:

ctypes.ArgumentError: argument 4: TypeError: expected CFunctionType instance instead of CFunctionType

This change makes CDataType_from_param_impl() report the expected and actual signatures when both sides are callback prototypes with argtypes set:

ctypes.ArgumentError: argument 4: TypeError: expected CFunctionType instance with signature (restype=<class 'ctypes.c_int'>, argtypes=(<class 'ctypes.c_void_p'>, <class 'ctypes.c_void_p'>)) instead of CFunctionType instance with signature (restype=<class 'ctypes.c_long'>, argtypes=(<class 'ctypes.c_void_p'>, <class 'ctypes.c_void_p'>))

Call behavior is unchanged; other mismatches keep the existing wording. Added test_mismatched_callback_prototype based on the qsort reproducer from the issue, plus a NEWS entry. ./python -m test test_ctypes passes on a Linux debug build.

AI assistance was used in preparing this change; I reviewed and tested it.

  • Issue: Ctypes: Unclear Error Message for WinFunctionType Mismatch in Windows API Calls #125788

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@aribaskagan
pythongh-125788: Improve ctypes error message for mismatched callback…
fd17c9a 
… prototypes

CFUNCTYPE and WINFUNCTYPE prototypes are distinct classes that share one
type name, so a mismatch was reported as "expected CFunctionType instance
instead of CFunctionType".  Include both signatures in the TypeError.

Co-authored-by: Kağan Arıbaş <[email protected]>
Copilot AI balanced review requested due to automatic review settings November 12, 2026 14:20
@python-cla-bot

python-cla-bot Bot commented Nov 12, 2026 •
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The following commit authors need to sign the Contributor License Agreement:

  • [email protected]

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@bedevere-app bedevere-app Bot added the type-feature A feature request or enhancement label Nov 12, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Nov 12, 2026
Ctypes: Unclear Error Message for WinFunctionType Mismatch in Windows API Calls #125788
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Copilot AI reviewed Nov 12, 2026

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Copilot was unable to review this pull request because the user who requested the review has insufficient remaining quota. Try requesting a review at a lower effort level.

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@chatgpt-codex-connector

chatgpt-codex-connector Bot commented Nov 12, 2026 •
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Codex Review Summary: ✅ Completed

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📝 Code Review ✅ Completed 2026-11-12T14:24:58.355484Z f6c92af PR opened
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@bedevere-app bedevere-app Bot added the awaiting review label Nov 12, 2026
@cursor
cursor Bot force-pushed the gh-125788-ctypes-callback-error branch from f6c92af to fd17c9a Compare November 12, 2026 17:02
@ZeroIntensity ZeroIntensity added the AI-needs-explanation AI-assisted work that needs further explanation and follow up from the contributor label Nov 12, 2026
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Thank you for your interest in contributing to Python. This is a community-driven project, and we want it to be a welcoming place to learn and collaborate.

Contributors are responsible for reviewing and understanding what they submit, checking its claims, and being able to explain changes in their own words. This helps reviewers focus on the contribution and leaves more time to support other contributors.

This contribution appears to have been authored with AI assistance. Please explain your contribution in your own words and describe how you checked its correctness.

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@aribaskagan @ZeroIntensity
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