Python 3.10 support? - undefined symbol: PyNode_ListTree

[SamuelMarks]

If it's not too early to request support :)

Error
Traceback (most recent call last):
  File "/opt/python3.10/lib/python3.10/unittest/case.py", line 59, in testPartExecutor
    yield
  File "/opt/python3.10/lib/python3.10/unittest/case.py", line 592, in run
    self._callTestMethod(testMethod)
  File "/opt/python3.10/lib/python3.10/unittest/case.py", line 549, in _callTestMethod
    method()

[omitted for brevity]

    from black import format_str, Mode
  File "lib/python3.10/site-packages/black/__init__.py", line 52, in <module>
    from typed_ast import ast3, ast27
  File "lib/python3.10/site-packages/typed_ast/ast3.py", line 40, in <module>
    from typed_ast import _ast3
ImportError: lib/python3.10/site-packages/typed_ast/_ast3.cpython-310d-x86_64-linux-gnu.so: undefined symbol: PyNode_ListTree
```

[hauntsaninja]

Well, it's certainly not too early to review a PR, if you're willing to provide one ;-) I'm guessing it's related to the removal of the old parser.

[gvanrossum]

Maybe you can copy listnode.c from earlier Python versions.

[gvanrossum]

It's just a debugging thing, you could also just comment out the one call.