But you definitely have idle installed, right? The commands earlier made an assumption about your installation that could be wrong, so that would explain it.

I'm still not entirely clear whether you've done these steps yet:

1. Right-click a .py file and select Open With
1a. If this gives you a deeper menu, select Another App
2. Find the Python launcher in the window that appears and select it.
3. Select Always Open with this app check box
4. Click Open/ok/whatever button is on there

That should reset your personal customization back to the original shortcut.