python-cartopy fails to build with Python 3.9.0a5.

=================================== FAILURES ===================================
_______________________ [doctest] cartopy.io.shapereader _______________________
022 
023     >>> import cartopy.io.shapereader as shapereader
024     >>> filename = shapereader.natural_earth(resolution='110m',
025     ...                                      category='physical',
026     ...                                      name='geography_regions_points')
027     >>> reader = shapereader.Reader(filename)
028     >>> len(reader)
029     3
030     >>> records = list(reader.records())
031     >>> print(', '.join(str(r) for r in sorted(records[0].attributes.keys())))
Expected:
    comment, ... name, name_alt, ... region, ...
Got nothing

/builddir/build/BUILDROOT/python-cartopy-0.18.0~b1-1.fc33.x86_64/usr/lib64/python3.9/site-packages/cartopy/io/shapereader.py:31: DocTestFailure
_____________________________ test_transform_point _____________________________

    def test_transform_point():
        """
        Mostly tests the workaround for a specific problem.
        Problem report in: https://github.com/SciTools/cartopy/issues/23
        Fix covered in: https://github.com/SciTools/cartopy/pull/277
        """
    
        # this way has always worked
        result = _CRS_ROB.transform_point(35.0, 70.0, _CRS_PC)
>       assert_array_almost_equal(result, (2376187.27182751, 7275317.81573085),
                                  _TOL)
E       AssertionError: 
E       Arrays are not almost equal to 7 decimals
E       
E       Mismatched elements: 2 / 2 (100%)
E       Max absolute difference: 0.30056718178093433
E       Max relative difference: 4.131327172141421e-08
E        x: array([ 2376187.2182271,  7275318.116298 ])
E        y: array([ 2376187.2718275,  7275317.8157309])

../../BUILDROOT/python-cartopy-0.18.0~b1-1.fc33.x86_64/usr/lib64/python3.9/site-packages/cartopy/tests/crs/test_robinson.py:126: AssertionError
____________________________ test_transform_points _____________________________

    def test_transform_points():
        """
        Mostly tests the workaround for a specific problem.
        Problem report in: https://github.com/SciTools/cartopy/issues/23
        Fix covered in: https://github.com/SciTools/cartopy/pull/277
        """
    
        # these always worked
        result = _CRS_ROB.transform_points(_CRS_PC,
                                           np.array([35.0]),
                                           np.array([70.0]))
>       assert_array_almost_equal(result,
                                  [[2376187.27182751, 7275317.81573085, 0]], _TOL)
E       AssertionError: 
E       Arrays are not almost equal to 7 decimals
E       
E       Mismatched elements: 2 / 3 (66.7%)
E       Max absolute difference: 0.30056718178093433
E       Max relative difference: 4.131327172141421e-08
E        x: array([[ 2376187.2182271,  7275318.116298 ,        0.       ]])
E        y: array([[ 2376187.2718275,  7275317.8157309,        0.       ]])

../../BUILDROOT/python-cartopy-0.18.0~b1-1.fc33.x86_64/usr/lib64/python3.9/site-packages/cartopy/tests/crs/test_robinson.py:149: AssertionError

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.9/fedora-rawhide-x86_64/01321079-python-cartopy/

For all our attempts to build python-cartopy with Python 3.9, see:
https://copr.fedorainfracloud.org/coprs/g/python/python3.9/package/python-cartopy/

Testing and mass rebuild of packages is happening in copr. You can follow these instructions to test locally in mock if your package builds with Python 3.9:
https://copr.fedorainfracloud.org/coprs/g/python/python3.9/

Let us know here if you have any questions.

Python 3.9 will be included in Fedora 33. To make that update smoother, we're building Fedora packages with early pre-releases of Python 3.9.
A build failure prevents us from testing all dependent packages (transitive [Build]Requires), so if this package is required a lot, it's important for us to get it fixed soon.
We'd appreciate help from the people who know this package best, but if you don't want to work on this now, let us know so we can try to work around it on our side.