consider to use python type hints syntax

[sbernard31]

To facilitate refactoring, maybe it could make sense to use type hints to allow us to static type checking.

see :

• https://docs.python.org/3/library/typing.html
• http://mypy-lang.org/
• https://realpython.com/python-type-checking
• https://medium.com/@ageitgey/learn-how-to-use-static-type-checking-in-python-3-6-in-10-minutes-12c86d72677b