> If you just want to add a workaround in dash_R_cleanup, I think it would be better to generate the list of all abstract classes and add three typing classes to it.

Yes, I just updated the PR.

I have found something else unrelated to typing, this test (in exactly this order):

./python -m test -R 5:5 test_abc test_functools

fails with a reproducible pattern:

test_functools leaked [0, 3, 1, 0, 0] memory blocks, sum=4

If you are happy with the PR now, we could open two separate issues for possible bug in inspect.isabstract and refleak in test_functools after test_abc. (the latter however might be potentially somehow related to abc caches)