Test failure on aarch64 in test_contour_level_diag_0 with PlotPy 2.4.0

[ema]

In Debian we are seeing a test failure with PlotPy 2.4.0 on aarch64: https://bugs.debian.org/1075814

____________________ ContourTest.test_contour_level_diag_0 _____________________

self = <plotpy.tests.unit.test_contour.ContourTest testMethod=test_contour_level_diag_0>

    def test_contour_level_diag_0(self):
        """Test that contour() returns opened lines (diagonal) when level is 0.0"""
        lines = compute_contours(self.Z, 0.0, self.X, self.Y)
>       assert len(lines) == 1
E       assert 4 == 1
E        +  where 4 = len([<plotpy.items.contour.ContourLine object at 0xffffa7c0e4d0>, <plotpy.items.contour.ContourLine object at 0xffffa7c0cb...lotpy.items.contour.ContourLine object at 0xffffa7c0c0d0>, <plotpy.items.contour.ContourLine object at 0xffffa7c0d0d0>])

plotpy/tests/unit/test_contour.py:42: AssertionError

So lines is supposed to have only one element, but on aarch64 it has 4. I have inspected the contents of lines[0] and lines[1] hoping this could help find out what is going on. These are all the contents of lines[0]:

[[ 2.9    -1.9   ]
 [ 2.9125 -1.9125]
 [ 2.925  -1.925 ]
 [ 2.925  -1.925 ]
 [ 2.9375 -1.9375]
 [ 2.95   -1.95  ]
 [ 2.95   -1.95  ]
 [ 2.9625 -1.9625]
 [ 2.975  -1.975 ]
 [ 2.9625 -1.9625]]

And the first few elements of lines[1] look like this:

[[-6.25000000e-02  1.06250000e+00]
 [-5.00000000e-02  1.05000000e+00]
 [-5.00000000e-02  1.05000000e+00]
 [-3.75000000e-02  1.03750000e+00]
 [-2.50000000e-02  1.02500000e+00]
 [-2.50000000e-02  1.02500000e+00]
 [...]

For reference, on a x86_64 system the first few elements of lines[0] are:

[[-9.75000000e-01  1.97500000e+00]
 [-9.62500000e-01  1.96250000e+00]
 [-9.50000000e-01  1.95000000e+00]
 [-9.50000000e-01  1.95000000e+00]
 [-9.37500000e-01  1.93750000e+00]
 [-9.25000000e-01  1.92500000e+00]
 [-9.25000000e-01  1.92500000e+00]
 [...]

The test failure can be reproduced reliably in the build tree as follows:

$ cd .pybuild/cpython3_3.12_plotpy/build
$ python3.12 -m pytest plotpy/tests/unit/test_contour.py

[PierreRaybaut]

@ema : FYI, I just released PlotPy v2.4.2 to fix this issue. Thanks again the feedback.