TypeAlias at python3.8 and python3.9

[rcmdnk]

Python3.8 does not allow alias with dict, list, tuple even with from __future__ import annotations

from __future__ import annotations


MyType = dict[str, str]

This shows an error like:

E   TypeError: 'type' object is not subscriptable

It can be written with typing.Dict (typing.List, typing.Tuple)

from __future__ import annotations

from typing import Dict


MyType = Dict[str, str]

This is OK even at python3.8.

This should be updated when python3.8 is dropped from the support.

From python3.10, typing.TypeAlias is introduced to declare aliases.

But it can not be imported by from __future__ import annotations.
It can be used when only >=python3.10 is supported.