You would probably enjoy the `port select` command in Macports to pick the version you want to launch when invoking, say, "python". Macports is also good about

You would probably enjoy the `port select` command in Macports to pick the version you want to launch when invoking, say, "python". Macports is also good about naming different versions, so you can have python-34, python-37, and python-29 installed together.