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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.