Remember that there are two sets of locations - HKCU and HKLM - where the type associations are potentially held. Please do a registry search (with Administrator rights so you can search the whole registry) for "py.exe" or "pyw.exe" and see if they show up anywhere at all. The launcher code tries to add these keys in HKEY_CLASSES_ROOT, but I believe Windows can map this to HKCU rather than HKLM if you don't have administrator access, at least on XP.