Python Setup and Usage, 3.3.1. Excursus: Setting environment variables
https://docs.python.org/3/using/windows.html#excursus-setting-environment-variables

The word 'excursus' is so rare and archaic that this is my first encounter with it.  Could we drop it?

The last paragraph starts with "To permanently modify the default environment variables, click Start and search for ‘edit environment variables’,".  This part is fine on Windows 10 as it brings up "Edit the system environment variables" and "Edit environmental variables for your account".  Both take one to an Environmental variables dialog.  The former requires than one be or become an admin user (via UAC dialog). 

The paragraph continues "or open System properties, Advanced system settings and click the Environment Variables button. In this dialog, you can add or modify User and System variables. To change System variables, you need non-restricted access to your machine (i.e. Administrator rights)."

On Windows 10, at least, this is confusing or wrong.  Control Panel has 'System' linked to the System dialog.  This has 'Advanced systems settings' linked to System Properties, but one only get there by being or becoming (via UAC) an admin user.  This has the  Environmental Properties button mentioned above.  It opens Environmental Variables for the admin user you are or are acting as.  This route cannot change EVs for non-admin users.  I have the impression that this has changed since Win 7.