I wanted to use the 32 bits python because I need a module that only works with the 32 bits version, but I don't want to use the 32 bits version always, but when I run a script, it runs with the 32 bits version, always. What can I do to only use the 32 bits sometimes, and leave the 64 bits for default use? Answer There are four different ways that Windows chooses which Python to run. If you type python or python foo.py at a DOS prompt, it goes by which one is found first on the PATH. Normally, the installer for each version puts that version at the start of your PATH, so whichever one you installed last wins. If you double-click foo.py in Explorer, it goes by Explorer's file type association mapping. Normally, the installer sets the association to its version, so again, whichever one you installed last wins. If the latest one you installed was new enough to have the "Python Windows Launcher", it will actually set that , rather than Python itself, as the Explorer ...