pytest.approx(Decimal(...)) Causes decimal.FloatOperation in __repr__ (pytest 8.4.0+)

[rishid]

pytest.approx() with decimal.Decimal objects triggers a decimal.FloatOperation error when the ApproxDecimal object's repr method is called (e.g., during print() or assertion formatting).

This happens because ApproxDecimal.repr compares its Decimal tolerance with hardcoded float literals (like 1e-3, 1e3). When the decimal context traps FloatOperations (to maintain Decimal precision), these implicit float-Decimal comparisons raise an error.

This issue started with pytest version 8.4.0 and seems related to changes from Issue #13010.

Pytest 8.4.0
Python 3.13.2
Ubuntu 24.04 LTS

# test_decimal_approx.py
import decimal

import pytest

decimal.getcontext().traps[decimal.FloatOperation] = True


def test_decimal_approx_repr_issue():
    """Reproduces the decimal.FloatOperation error from pytest.approx(Decimal)'s repr."""
    approx_obj = pytest.approx(decimal.Decimal("2.60"))
    print(f"Attempting to represent pytest.approx(Decimal): {approx_obj}")  # Triggers the bug
    assert decimal.Decimal("2.600001") == approx_obj


# You can run this test with:
# python -m pytest test_decimal_approx.py

[RonnyPfannschmidt]

Thanks for the details

We where completely unaware

This needs a unittests that triggers it locally

I suspect it was missed before in the general error case and the referred change made it manifest

Would you like to try your hand in contributing a gix as you seem to work with the details in more depth than we

[coder-aditi]

Hello @RonnyPfannschmidt , understanding the issue, I committed a fix, please review it and let me know your thoughts or any changes required.

[coder-aditi]

Hello @RonnyPfannschmidt , @nicoddemus , I made the necessary changes you guys suggested and committed in a new branch (was facing some branch conflicts, please have a look

PR -> #13543