gh-155526: Don't check errno in abs(complex) (#155527) · python/cpython@e5d4fa2 · GitHub
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gh-155526: Don't check errno in abs(complex) (#155527)
abs(complex) no longer raises OverflowError if errno was set to ERANGE by some library call but abs() doesn't overflow. _Py_c_abs() no longer sets errno to zero on success, but rather leaves it unchanged. Co-authored-by: Victor Stinner <vstinner@python.org> Co-authored-by: hpkfft.com <paul@hpkfft.com>
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Lines changed: 76 additions & 19 deletions

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‎Doc/c-api/complex.rst‎

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‎Doc/whatsnew/3.16.rst‎

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@@ -1018,6 +1018,10 @@ Porting to Python 3.16
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if the value cannot be marshalled.
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(Contributed by Serhiy Storchaka in :gh:`155907`.)
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* :c:func:`_Py_c_abs` no longer sets :c:data:`errno` to zero on success,
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but rather leaves it unchanged.
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(Contributed by Sergey B Kirpichev in :gh:`155526`.)
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Deprecated C APIs
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-----------------
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‎Lib/test/test_capi/test_complex.py‎

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@@ -281,18 +281,34 @@ def test_py_c_abs(self):
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# Test _Py_c_abs()
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_py_c_abs = _testcapi._py_c_abs
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self.assertEqual(_py_c_abs(-1), (1.0, 0))
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self.assertEqual(_py_c_abs(1j), (1.0, 0))
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self.assertEqual(_py_c_abs(complex('+inf+1j')), (INF, 0))
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self.assertEqual(_py_c_abs(complex('-inf+1j')), (INF, 0))
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self.assertEqual(_py_c_abs(complex('1.25+infj')), (INF, 0))
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self.assertEqual(_py_c_abs(complex('1.25-infj')), (INF, 0))
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self.assertTrue(isnan(_py_c_abs(complex('1.25+nanj'))[0]))
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self.assertTrue(isnan(_py_c_abs(complex('nan-1j'))[0]))
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self.assertEqual(_py_c_abs(complex(*[DBL_MAX]*2))[1], errno.ERANGE)
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def c_abs(num):
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# On success, _Py_c_abs() doesn't use errno and leaves errno
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# unchanged
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_testcapi.set_errno(0)
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result, errno = _py_c_abs(num)
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self.assertEqual(errno, 0)
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return result
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try:
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self.assertEqual(c_abs(-1), 1.0)
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self.assertEqual(c_abs(1j), 1.0)
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self.assertEqual(c_abs(complex('+inf+1j')), INF)
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self.assertEqual(c_abs(complex('-inf+1j')), INF)
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self.assertEqual(c_abs(complex('1.25+infj')), INF)
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self.assertEqual(c_abs(complex('1.25-infj')), INF)
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self.assertTrue(isnan(c_abs(complex('1.25+nanj'))))
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self.assertTrue(isnan(c_abs(complex('nan-1j'))))
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# Set errno to ERANGE on overflow
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_testcapi.set_errno(0)
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self.assertEqual(_py_c_abs(complex(*[DBL_MAX]*2)),
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(INF, errno.ERANGE))
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# Preserve errno on success
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_testcapi.set_errno(errno.EACCES)
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self.assertEqual(_py_c_abs(1j), (1.0, errno.EACCES))
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finally:
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_testcapi.set_errno(0)
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if __name__ == "__main__":

‎Lib/test/test_complex.py‎

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@@ -1,6 +1,8 @@
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import errno
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import unittest
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import sys
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from test import support
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from test.support import import_helper
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from test.support.testcase import ComplexesAreIdenticalMixin
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from test.support.numbers import (
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VALID_UNDERSCORE_LITERALS,
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from random import random
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from math import isnan, copysign
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import cmath
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import operator
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INF = float("inf")
@@ -860,8 +863,30 @@ def test_abs(self):
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for num in nums:
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self.assertAlmostEqual((num.real**2 + num.imag**2) ** 0.5, abs(num))
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for x in 0.0, -0.0, INF, -INF, NAN:
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for y in 0.0, -0.0, INF, -INF, NAN:
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with self.subTest(x=x, y=y):
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z = complex(x, y)
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r = abs(z)
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if cmath.isfinite(z):
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self.assertFloatsAreIdentical(r, 0.0)
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elif cmath.isinf(z):
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self.assertEqual(r, INF)
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else:
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self.assertTrue(cmath.isnan(z))
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self.assertTrue(isnan(r))
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self.assertRaises(OverflowError, abs, complex(DBL_MAX, DBL_MAX))
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def test_abs_errno_handling(self):
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_testcapi = import_helper.import_module('_testcapi')
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z = complex('nan')
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_testcapi.set_errno(errno.ERANGE)
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try:
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self.assertTrue(isnan(abs(z)))
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finally:
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_testcapi.set_errno(0)
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def test_repr_str(self):
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def test(v, expected, test_fn=self.assertEqual):
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test_fn(repr(v), expected)

‎Misc/NEWS.d/next/C_API/2026-09-10-15-19-16.gh-issue-155526.kMKhyp.rst‎

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:c:func:`_Py_c_abs` no longer sets :c:data:`errno` to zero on success, but
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rather leaves it unchanged. Patch by Sergey B Kirpichev.

‎Misc/NEWS.d/next/Core_and_Builtins/2026-08-11-06-04-26.gh-issue-155526.W7ZHXu.rst‎

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Fix spurious :exc:`OverflowError` for ``abs(nanj)`` in case :c:data:`errno` was
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previously set to :c:macro:`!ERANGE` by some library call.
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Patch by Sergey B Kirpichev.

‎Modules/_testcapi/complex.c‎

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@@ -76,7 +76,6 @@ _py_c_abs(PyObject *Py_UNUSED(module), PyObject* obj)
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return NULL;
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}
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errno = 0;
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res = _Py_c_abs(complex);
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return Py_BuildValue("di", res, errno);
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}

‎Modules/cmathmodule.c‎

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@@ -1029,8 +1029,8 @@ cmath_polar_impl(PyObject *module, Py_complex z)
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{
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double r, phi;
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errno = 0;
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phi = atan2(z.imag, z.real); /* should not cause any exception */
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errno = 0;
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r = _Py_c_abs(z); /* sets errno to ERANGE on overflow */
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if (errno != 0)
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return math_error();

‎Objects/complexobject.c‎

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