python-joblib fails to build with Python 3.10.0a5.

=================================== FAILURES ===================================
_______________________________ test_direct_mmap _______________________________
joblib.externals.loky.process_executor._RemoteTraceback: 
"""
Traceback (most recent call last):
  File "/builddir/build/BUILD/joblib-1.0.1/joblib/externals/loky/process_executor.py", line 431, in _process_worker
    r = call_item()
  File "/builddir/build/BUILD/joblib-1.0.1/joblib/externals/loky/process_executor.py", line 285, in __call__
    return self.fn(*self.args, **self.kwargs)
  File "/builddir/build/BUILD/joblib-1.0.1/joblib/_parallel_backends.py", line 595, in __call__
    return self.func(*args, **kwargs)
  File "/builddir/build/BUILD/joblib-1.0.1/joblib/parallel.py", line 262, in __call__
    return [func(*args, **kwargs)
  File "/builddir/build/BUILD/joblib-1.0.1/joblib/parallel.py", line 262, in <listcomp>
    return [func(*args, **kwargs)
  File "/builddir/build/BUILD/joblib-1.0.1/joblib/test/test_memmapping.py", line 1314, in worker
  File "/builddir/build/BUILD/joblib-1.0.1/joblib/test/test_memmapping.py", line 1142, in _read_array
    mm = mmap.mmap(fd.fileno(), 0, access=mmap.ACCESS_READ, offset=0)
NameError: name 'open' is not defined
"""

The above exception was the direct cause of the following exception:

tmpdir = local('/tmp/pytest-of-mockbuild/pytest-0/test_direct_mmap0')

    @with_numpy
    @with_multiprocessing
    def test_direct_mmap(tmpdir):
        testfile = str(tmpdir.join('arr.dat'))
        a = np.arange(10, dtype='uint8')
        a.tofile(testfile)
    
        def _read_array():
            with open(testfile) as fd:
                mm = mmap.mmap(fd.fileno(), 0, access=mmap.ACCESS_READ, offset=0)
            return np.ndarray((10,), dtype=np.uint8, buffer=mm, offset=0)
    
        def func(x):
            return x**2
    
        arr = _read_array()
    
        # this is expected to work and gives the reference
        ref = Parallel(n_jobs=2)(delayed(func)(x) for x in [a])
    
        # now test that it work with the mmap array
        results = Parallel(n_jobs=2)(delayed(func)(x) for x in [arr])
        np.testing.assert_array_equal(results, ref)
    
        # also test with a mmap array read in the subprocess
        def worker():
            return _read_array()
    
>       results = Parallel(n_jobs=2)(delayed(worker)() for _ in range(1))

joblib/test/test_memmapping.py:1161: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
joblib/parallel.py:1054: in __call__
    self.retrieve()
joblib/parallel.py:933: in retrieve
    self._output.extend(job.get(timeout=self.timeout))
joblib/_parallel_backends.py:542: in wrap_future_result
    return future.result(timeout=timeout)
/usr/lib64/python3.10/concurrent/futures/_base.py:440: in result
    return self.__get_result()
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <Future at 0x7f489963b5e0 state=finished raised NameError>

    def __get_result(self):
        if self._exception:
>           raise self._exception
E           NameError: name 'open' is not defined

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.10/fedora-rawhide-x86_64/01957550-python-joblib/

For all our attempts to build python-joblib with Python 3.10, see:
https://copr.fedorainfracloud.org/coprs/g/python/python3.10/package/python-joblib/

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 3.10:
https://copr.fedorainfracloud.org/coprs/g/python/python3.10/

Let us know here if you have any questions.

Python 3.10 will be included in Fedora 35. To make that update smoother, we're building Fedora packages with early pre-releases of Python 3.10.
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.