you should absolutely avoid overriding the default python installation if you're on a distribution that ships python2 by default in particular, because that is a good way to kill a good chunk of your system.
Everyone should depend on “python3” or “python2”, never just “python”. They aren’t really the same language. python3 can’t run python2 scripts, nor vice versa, so no matter what you expected there will be systems on which you won’t get it.