Declaring a `Optional[TypedDict]` fails at runtime

[rowillia]

For example, executing the following code results in a stack trace

from typing import Optional

from mypy_extensions import TypedDict

TaggedPoint = TypedDict('TaggedPoint', {'type': str, 'x': int, 'y': int})

def maybe_create_tagged_point() -> Optional[TaggedPoint]:
    return None

Traceback (most recent call last):
  File "test_runtime_typed_dict.py", line 7, in <module>
    def maybe_create_tagged_point() -> Optional[TaggedPoint]:
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/typing.py", line 648, in __getitem__
    return Union[arg, type(None)]
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/typing.py", line 551, in __getitem__
    dict(self.__dict__), parameters, _root=True)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/typing.py", line 511, in __new__
    for t2 in all_params - {t1} if not isinstance(t2, TypeVar)):
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/typing.py", line 511, in <genexpr>
    for t2 in all_params - {t1} if not isinstance(t2, TypeVar)):
  File "/Users/rwilliams/src/oss/mypy/venv/src/mypy-extensions/extensions/mypy_extensions.py", line 20, in _check_fails
    raise TypeError('TypedDict does not support instance and class checks')
TypeError: TypedDict does not support instance and class checks

[refi64]

Should this be instead reported to python/typing?

[refi64]

https://github.com/python/typing

[rowillia]

@kirbyfan64 TypedDict is not yet part of typing