tests/test_xpath1_parser.py::LxmlXPath1ParserTest::test_sum_function fails on some systems

[mgorny]

This is basically a "sigh" kind of problem but when running on my production system, I'm getting the following test failure:

_______________________________________________ LxmlXPath1ParserTest.test_sum_function ________________________________________________

self = <tests.test_xpath1_parser.LxmlXPath1ParserTest testMethod=test_sum_function>

    def test_sum_function(self):
        root = self.etree.XML(XML_DATA_TEST)
        context = XPathContext(root, variables=self.variables)
        self.check_value("sum($values)", 35, context)
        if sys.version_info < (3, 12):
            self.check_selector("sum(/values/a)", root, 13.299999999999999)
        else:
>           self.check_selector("sum(/values/a)", root, 13.3)

context    = XPathContext(root=<Element values at 0x7f63e26e3540>)
root       = <Element values at 0x7f63e26e3540>
self       = <tests.test_xpath1_parser.LxmlXPath1ParserTest testMethod=test_sum_function>

tests/test_xpath1_parser.py:1136: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
tests/test_xpath1_parser.py:1683: in check_selector
    self.assertEqual(root.xpath(path, namespaces=namespaces, **variables), expected)
E   AssertionError: 13.299999999999999 != 13.3
        expected   = 13.3
        kwargs     = {}
        namespaces = None
        path       = 'sum(/values/a)'
        results    = 13.3
        root       = <Element values at 0x7f63e26e3540>
        self       = <tests.test_xpath1_parser.LxmlXPath1ParserTest testMethod=test_sum_function>
        variables  = {}

However, in the tox venv it's passing.

I've seen another package having weird precision-related test failure with Python 3.12. Perhaps the right solution would be to do testing with some tolerance rather than assuming an exact value?

[brunato]

Hi,
i will take a look soon for this. Probably your suggestion should be the right decision.

[hroncok]

This fails in Fedora on multiple architectures. I believe it might be related to python/cpython#100425

[hroncok]

Oh, sorry but we don't have 81bca86 in Fedora yet, so perhaps I am not hitting the same problem but an older reversed one.

[hroncok]

Expecting 13.3 on Python 3.12.0b2 works in Fedora on many tests but one. I agree that rather than if'ing the expected number, asserting the numbers are close seems better. E.g. via assertAlmostEqual.

[brunato]

Release v4.1.3 test helpers (check_value and check_selector) use assertAlmostEqual if the provided expected argument is a float number.

This should be enough to avoid approximation errors in tests (apply it also to decimal.Decimal values shouldn't be necessary).

[mgorny]

Thanks. I can confirm that the tests pass for me in 4.1.3.