#### Description of the problem <!--Please provide a clear and details information of the bug/data structure to be added.--> From now onwards, the new code should use `typing` module and the existing code in `master` should be modified to use `typing` module. #### Example of the problem <!--Provide a reproducible example code which is causing the bug to appear. Leave this section if the problem is not a bug.--> #### References/Other comments See, https://docs.python.org/3/library/typing.html