test.test_math.MathTests.testAtan2 failure on OpenIndiana/Solaris

I do see the following failure with Python-3.14.0rc2 on OpenIndiana. This is a regression from Python-3.13.7.

======================================================================
ERROR: testAtan2 (test.test_math.MathTests.testAtan2)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/data/builds/ul-workspace/components/python/python-314/Python-3.14.0rc2/Lib/test/test_math.py", line 339, in testAtan2
    self.ftest('atan2(0., -0.)', math.atan2(0., -0.), math.pi)
                                 ~~~~~~~~~~^^^^^^^^^
ValueError: math domain error

----------------------------------------------------------------------

Linked PRs

@kulikjak

Also occurs on our Solaris buildbot.

I actually talked about this with @kulikjak, and this is an issue on their side. So there isn't anything for us to do.

Does that mean we should close this?

@mtelka

math.atan2 is essentially a thin wrapper over libm's atan2:

cpython/Modules/mathmodule.c

Lines 1100 to 1103 in 8554c09

    
           FUNC2(atan2, atan2, 
        
                 "atan2($module, y, x, /)\n--\n\n" 
        
                 "Return the arc tangent (measured in radians) of y/x.\n\n" 
        
                 "Unlike atan(y/x), the signs of both x and y are considered.")

cpython/Modules/mathmodule.c

Lines 1014 to 1047 in 8554c09

    
           static PyObject * 
        
           math_2(PyObject *const *args, Py_ssize_t nargs, 
        
                  double (*func) (double, double), const char *funcname) 
        
           { 
        
               double x, y, r; 
        
               if (!_PyArg_CheckPositional(funcname, nargs, 2, 2)) 
        
                   return NULL; 
        
               x = PyFloat_AsDouble(args[0]); 
        
               if (x == -1.0 && PyErr_Occurred()) { 
        
                   return NULL; 
        
               } 
        
               y = PyFloat_AsDouble(args[1]); 
        
               if (y == -1.0 && PyErr_Occurred()) { 
        
                   return NULL; 
        
               } 
        
               errno = 0; 
        
               r = (*func)(x, y); 
        
               if (isnan(r)) { 
        
                   if (!isnan(x) && !isnan(y)) 
        
                       errno = EDOM; 
        
                   else 
        
                       errno = 0; 
        
               } 
        
               else if (isinf(r)) { 
        
                   if (isfinite(x) && isfinite(y)) 
        
                       errno = ERANGE; 
        
                   else 
        
                       errno = 0; 
        
               } 
        
               if (errno && is_error(r, 1)) 
        
                   return NULL; 
        
               else 
        
                   return PyFloat_FromDouble(r); 
        
           }

I don't think something was changed here since v3.13 other than using libm's isinf/isnan macro directly.

It looks like in the given case platform's atan2 returns a nan. @mtelka, could you verify this?

Correct answer is pi, see https://en.cppreference.com/w/c/numeric/math/atan2.html (Assuming IEEE 754-compatible behavior.) @mtelka, did you test on same version of the OS? This looks as a regression for me, but not in the CPython.

Edit: I assume, that we won't add a workaround for unsupported broken platform. Or?

math.atan2 is essentially a thin wrapper over libm's atan2:

Yes, as I said, this is an issue in their library, which they hope to fix soon.

Ok, let's close. I don't think workaround is needed.

I tested this simple C:

#include <math.h>
#include <stdio.h>

int main(void)
{
        printf("%f\n", atan2(0., -0.));
        return 0;
}

and here is the result:

$ gcc -Wall -o test test.c 
$ ./test 
3.141593
$

How can I prove the issue is with the platform?

pythongh-138573: filter out failing math tests on Solaris

@mtelka

@mtelka, see #146402.

(I found mentions of this behavior on our bug tracker from 1988)

Wow, this is an old bug! 😄

For completeness, here is list of failed tests on OpenIndiana with Python 3.13.7:

6 tests failed:
test.test_asyncio.test_ssl test_cext test_cppext test_embed
test_shutil test_socket

I'm interested by test_cext and test_cppext failures, but also by test_embed failure. Would you mind to open an issue for test_cext+test_cppext and another one for test_embed?

gh-138573: Filter out failing math tests on Solaris (#146402)

pythongh-138573: Filter out failing math tests on Solaris (pythonGH-1…

@mtelka

The two failing tests are now skipped on Solaris: 8e1469c. The change will be backported to 3.14 once the CI pass on the PR.

Thanks for your bug report @mtelka.

Okay, it looks like the issue is really with the platform, so I reported the bug at https://www.illumos.org/issues/17602.

Oh, this issue has been fixed by the change illumos/illumos-gate@2eba8eb in the meanwhile, nice!

We do have only one libm implementation, so yes.

What is lib_version != libm_ieee test in the implementation? It's possible to select a "lib_version" to get different behaviors?

[3.14] gh-138573: Filter out failing math tests on Solaris (GH-146402) (

We do have only one libm implementation, so yes.

What is lib_version != libm_ieee test in the implementation? It's possible to select a "lib_version" to get different behaviors?

I do not think so. However, there was a discussion about this line during the code review. You can find it here: https://code.illumos.org/c/illumos-gate/+/4476

I'm interested by test_cext and test_cppext failures, but also by test_embed failure. Would you mind to open an issue for test_cext+test_cppext and another one for test_embed?

These tests pass with Python 3.14.3.

Thank you for the merge. We still didn't fix (or change) the atan2 behavior, so the skip at least helps us.

pythongh-138573: Filter out failing math tests on Solaris (python#146402

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`test.test_math.MathTests.testAtan2` failure on OpenIndiana/Solaris #138573

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	FUNC2(atan2, atan2,
	"atan2($module, y, x, /)\n--\n\n"
	"Return the arc tangent (measured in radians) of y/x.\n\n"
	"Unlike atan(y/x), the signs of both x and y are considered.")

	static PyObject *
	math_2(PyObject const args, Py_ssize_t nargs,
	double (func) (double, double), const char funcname)
	{
	double x, y, r;
	if (!_PyArg_CheckPositional(funcname, nargs, 2, 2))
	return NULL;
	x = PyFloat_AsDouble(args[0]);
	if (x == -1.0 && PyErr_Occurred()) {
	return NULL;
	}
	y = PyFloat_AsDouble(args[1]);
	if (y == -1.0 && PyErr_Occurred()) {
	return NULL;
	}
	errno = 0;
	r = (*func)(x, y);
	if (isnan(r)) {
	if (!isnan(x) && !isnan(y))
	errno = EDOM;
	else
	errno = 0;
	}
	else if (isinf(r)) {
	if (isfinite(x) && isfinite(y))
	errno = ERANGE;
	else
	errno = 0;
	}
	if (errno && is_error(r, 1))
	return NULL;
	else
	return PyFloat_FromDouble(r);
	}

test.test_math.MathTests.testAtan2 failure on OpenIndiana/Solaris #138573

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StanFromIreland commented on Sep 6, 2025

terryjreedy commented on Sep 6, 2025

skirpichev commented on Sep 6, 2025

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mtelka commented on Sep 6, 2025

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`test.test_math.MathTests.testAtan2` failure on OpenIndiana/Solaris #138573