Support for type hints

[yhay81]

Some files have type hints and others do not.
I think writing type hints make it easier to understand the patterns.
I suggest to write type hints and if its okay, I will work some.

And there are two typing style now in python, so I would ask which is good, >=3.9 style or <3.9 style.
(mypy started to support for >=3.9 style just two days ago. https://mypy-lang.blogspot.com/2021/01/mypy-0800-released.html)

[faif]

Hi. Another contributor started adding type hints that's why some files have hints and some not. Feel free to continue with that but let's stick to <3.9 for now.

[cdorsman]

What is the stance now about type hints?

It is four years later and type hints is more ingrained in general Python development than it was back then. And 3.9 is EOL somewhere this year.