related to https://bugs.python.org/issue35311

encountered here: https://gitlab.com/pycqa/flake8/issues/473

minimal reproduction:


class TestPickleableException(unittest.TestCase):
    def test_ParseError(self):
        err = ParseError('msg', 2, None, (1, 'context'))
        err2 = pickle.loads(pickle.dumps(err))
        self.assertEqual(vars(err), vars(err2))


======================================================================
ERROR: test_ParseError (lib2to3.tests.test_parser.TestPickleableException)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/asottile/workspace/cpython/Lib/lib2to3/tests/test_parser.py", line 628, in test_ParseError
    err2 = pickle.loads(pickle.dumps(err))
TypeError: __init__() missing 3 required positional arguments: 'type', 'value', and 'context'