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.
Replace python with many other tools from Java, node, etc.