Problem with Python 3.9.0a5

[ok2]

I have tried to test my application on Python 3.9.0 alpha 5, may be it is just a bug of the unstable python, but I get strange error, here small program to reproduce:

from typing import List
def a1(b: List[int]) -> int:
    return b[0]

Starting that:

(py39) $ mypy --show-error-context --pretty --strict test.py
test.py:2: error: syntax error in type comment
    def a1(b: List[int]) -> int:
              ^
Found 1 error in 1 file (checked 1 source file)

On python 3.8 environment it works without any problems.

[hauntsaninja]

This is a known issue that is fixed on mypy master (#8627)