I'm desperately in need of a guide on how to un-fuck my Python setup. On my Mac I have several versions of the default shipped Python, brew-installed versions of 2 and 3, and Anaconda-installed versions of 2 and 3, and I have no idea which I'm getting when I call 'python3' or 'ipython', or what should be being used. Substitute brew for apt and it's the same situation on Ubuntu. It's really confusing and means I have to troubleshoot dependencies for any Python project I try to run.