=== Manually Defining Explicit Python Binary Executables ===
A common practice is to have a bunch of specific Python commands to force explicit behavior. For example on Ubuntu, you can choose from running python, python2, python 2.6, python2.7, python3, python3.5, etc in the shell. To emulate this behavior, copy and paste the <code>python.exe</code> and rename it to <code>pythonN.exe</code> where N is whatever specific version you copied. The same applies to scripts you want to use like <code>pip</code>: copy-and-paste the file to a more explicit name.
Path is evaluated with the first entries taking precedence. Thus, whichever version of Python you want to be the default should be listed at the leftmost position on the string. You can also just delete the unregistered python.exe to achieve the same result.