You are working on project A, and project B. Project A uses python 2.6, project B uses python 3. You want a simple way to switch back and forth without reinstal

You are working on project A, and project B. Project A uses python 2.6, project B uses python 3. You want a simple way to switch back and forth without reinstalling everything every time you switch between them. This setups a way to quickly and if I'm understanding correctly automatically switching between the two versions of the tool. Replace python with many other tools from Java, node, etc.