diffoscope fails to build with Python 3.9.0a3.

_____________________________ test_identification ______________________________
file1 = <<class 'diffoscope.comparators.binary.FilesystemFile'> /builddir/build/BUILD/diffoscope-134/tests/data/test1.ppu>
    @skip_unless_tools_exist('ppudump')
    def test_identification(file1):
>       assert isinstance(file1, PpuFile)
E       AssertionError: assert False
E        +  where False = isinstance(<<class 'diffoscope.comparators.binary.FilesystemFile'> /builddir/build/BUILD/diffoscope-134/tests/data/test1.ppu>, PpuFile)
tests/comparators/test_ppu.py:50: AssertionError
__________________________ test_compare_non_existing ___________________________
monkeypatch = <_pytest.monkeypatch.MonkeyPatch object at 0x7efe027c2ca0>
file1 = <<class 'diffoscope.comparators.binary.FilesystemFile'> /builddir/build/BUILD/diffoscope-134/tests/data/test1.ppu>
    @skip_unless_tool_is_at_least('ppudump', ppudump_version, '3.0.0')
    def test_compare_non_existing(monkeypatch, file1):
>       assert_non_existing(monkeypatch, file1, has_null_source=False)
tests/comparators/test_ppu.py:71: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
monkeypatch = <_pytest.monkeypatch.MonkeyPatch object at 0x7efe027c2ca0>
fixture = <<class 'diffoscope.comparators.binary.FilesystemFile'> /builddir/build/BUILD/diffoscope-134/tests/data/test1.ppu>
has_null_source = False, has_details = True
    def assert_non_existing(
        monkeypatch, fixture, has_null_source=True, has_details=True
    ):
        monkeypatch.setattr(Config(), 'new_file', True)
        assert Config().new_file, "Did not get patched"
    
        difference = fixture.compare(MissingFile('/nonexisting', fixture))
    
        assert difference.source2 == '/nonexisting'
>       assert not has_details or len(difference.details) > 0
E       AssertionError
tests/utils/nonexisting.py:34: AssertionError

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.9/fedora-rawhide-x86_64/01206343-diffoscope/

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

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.