Drop redundant exception type prefix from float-to-int error messages by changjoon-park · Pull Request #7763 · RustPython/RustPython

changjoon-park · 2026-05-02T11:36:30Z

Summary

CPython raises OverflowError("cannot convert float infinity to integer") and ValueError("cannot convert float NaN to integer") (Objects/floatobject.c). The exception type name is added by Python's traceback display layer; the message itself should not duplicate it.

try_to_bigint was producing the duplicated form:

>>> int(float("inf"))
# CPython 3.14.4: OverflowError('cannot convert float infinity to integer')
# RustPython main: OverflowError('OverflowError: cannot convert float infinity to integer')  ❌

This makes repr(e) and any code path that inspects str(e) diverge from CPython.

Affected sites

All five callers of try_to_bigint share the message:

Operation	Caller
`int(x)`	`float.__int__`
`math.floor(x)`	`float.__floor__`
`math.ceil(x)`	`float.__ceil__`
`math.trunc(x)`	`float.__trunc__`
`round(x)` (no ndigits)	`float.__round__`

Verification

Byte-identical with CPython 3.14.4 across 14 probe sites: 14/14 match.
cargo run --release -- -m test test_float test_builtin test_math test_int test_long test_complex test_decimal test_fractions test_statistics test_format test_re — 1,627 tests pass, 0 regressions.
All 188 extra_tests/snippets/*.py pass under the CI feature set.

A regression block is added to extra_tests/snippets/builtin_float.py checking the exact message text via a small _check_msg(call, exc_type, expected_msg) helper across all five callers.

Summary by CodeRabbit

Release Notes

Bug Fixes
- Improved error messages when converting float infinity and NaN values to integers with standardized wording for consistency.
Tests
- Added comprehensive test coverage for float-to-integer conversion error messages across multiple conversion methods.

CPython raises `OverflowError("cannot convert float infinity to integer")` and `ValueError("cannot convert float NaN to integer")` from `Objects/floatobject.c::float___trunc___impl` and friends. The exception type name is added by Python's traceback display layer; the message itself should not duplicate it. `try_to_bigint` was producing `OverflowError("OverflowError: cannot convert ...")` etc., which made `repr(e)` and any code path that inspects `str(e)` diverge from CPython. Affects all 5 callers of `try_to_bigint`: `__int__`, `__floor__`, `__ceil__`, `__round__` (no-arg), `__trunc__` — i.e. `int(x)`, `math.floor/ceil/trunc(x)`, `round(x)` for non-finite floats. Verified byte-identical with CPython 3.14.4 across 14 affected sites.

coderabbitai · 2026-05-02T11:36:42Z

No actionable comments were generated in the recent review. 🎉

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📥 Commits

Reviewing files that changed from the base of the PR and between 926d69b and 32c9bf1.

📒 Files selected for processing (2)

crates/vm/src/builtins/float.rs
extra_tests/snippets/builtin_float.py

📝 Walkthrough

Walkthrough

Error messages for float-to-integer conversion failures are standardized to match CPython's exact wording. The try_to_bigint function removes error prefix strings and updates messages for infinity and NaN cases. Tests verify the standardized messages.

Changes

Float Conversion Error Standardization

Layer / File(s)	Summary
Error Message Update `crates/vm/src/builtins/float.rs`	`try_to_bigint` removes `"OverflowError:"` and `"ValueError:"` prefixes; updates messages to `"cannot convert float infinity to integer"` and `"cannot convert float NaN to integer"`.
Error Message Verification `extra_tests/snippets/builtin_float.py`	New `_check_msg` helper validates exact exception message text; assertions verify CPython-identical messages for `int()`, `round()`, `math.floor/ceil/trunc`, and dunder methods with `INF`, `-INF`, and `NAN`.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Suggested reviewers

youknowone
ShaharNaveh

Poem

🐰 Floats that soar to endless skies,
Now speak in standardized cries,
With messages clear, no prefix fuss,
CPython's tongue is ours to trust! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: removing redundant exception type prefixes from float-to-int error messages, which aligns with the core objective and file modifications.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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ShaharNaveh

huh, good catch!

changjoon-park · 2026-05-02T12:03:38Z

huh, good catch!

thanks for the review !

youknowone

👍

youknowone · 2026-05-04T01:24:02Z

@changjoon-park Just out of curiosity, are you finding bugs using fuzzing or other automated tools?

ShaharNaveh approved these changes May 2, 2026

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youknowone approved these changes May 4, 2026

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youknowone merged commit 181e4e7 into RustPython:main May 4, 2026
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Drop redundant exception type prefix from float-to-int error messages#7763

Drop redundant exception type prefix from float-to-int error messages#7763
youknowone merged 1 commit into
RustPython:mainfrom
changjoon-park:fix-float-to-int-error-prefix

changjoon-park commented May 2, 2026 •

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Summary

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changjoon-park commented May 2, 2026 •

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