Few type hints not compatible with python 3.9 & python 3.8

[raphaeljolivet]

Hi,

I just found that a few typing hints make the code not compatible with python3.9 & python3.8.
I guess those versions are still used a lot and it's too bad only a few lines make it not compatible.

I will do a PR to fix it.

BTW, I just discovered Tox for this: it enables you to package, deploy your lib and test it easily in several Python envs.
It's easy to use a handy to ensure broad compatibility.

[tngTUDOR]

@raphaeljolivet , the PR was merged. Do you think we can close this issue?