Traceback (most recent call last):

 "<stdin>", line 2, in <module>TypeError: issubclass() arg 2 must be a class or tuple of classes
Traceback (most recent call last):


 "/usr/lib/python3.8/threading.py", line 932, in _bootstrap_inner

self.run()


 "/usr/lib/python3.8/threading.py", line 870, in run

self._target(*self._args, **self._kwargs)


 "/builddir/build/BUILD/dask-2.18.0/dask/tests/test_threaded.py", line 135, in test_f

L.append(get(dsk, "y"))


 "/builddir/build/BUILD/dask-2.18.0/dask/threaded.py", line 72, in get

pool = ThreadPool(num_workers)


 "/usr/lib/python3.8/multiprocessing/pool.py", line 925, in __init__

Pool.__init__(self, processes, initializer, initargs)


 "/usr/lib/python3.8/multiprocessing/pool.py", line 216, in __init__

p.terminate()
AttributeError: 'DummyProcess' object has no attribute 'terminate'
