Would it be better to use, for example, python3 tag instead of python-3 because python3 is the command used to launch python3 on any operating system?
A related and interesting question is
Tagging Questions that involve Python programming language?
I would opt for sticking with python-3 because, as @MrXsquared has commented, there is a space between "Python" and "3" at the Python 3.0 Release home page.
Also, this would keep it aligned with other version tags used here like qgis-3, google-maps-api-3, arcgis-javascript-api-3, etc.
