How do I set IDLE as the default editor for Python scripts?

You didn't mention which idle package you are using, let's assume "Idle". If using "Idle3" then use idle3.desktop below. If using "Idle(using Python-2.7)" then use idle-python2.7.desktop

There are 2 things preventing you from finding idle in the context menus -

First none of the idle .desktops have a MimeType= line in them, that's why Idle doesn't show in the r. click > open with ... menu

Additionally - only .desktops whose Exec= line ends with a %letter will show in the r. click > properties context menu, even if they show up in the above 'open with' menu

So in this case easiest to just do this - first add to the open with menu

gedit ~/.local/share/applications/mimeapps.list

In the [Added Associations] section look for this line

text/x-python=

If there then add this to the end

idle.desktop;

If not there then just add

text/x-python=idle.desktop;

Idle should now be available in the open with menu, if not log out/in

While there, in the [Default Applications] section look for the same line & replace the .desktop as such, if not there just add the line ( no ; is used in the Defaults section

text/x-python=idle.desktop  

If Idle doesn't show up as the default, even after a restart then you'll need to 'force' it. I'd prefer this way rather than messing with defaults.list

open the .desktop in a root editor

 gksudo gedit /usr/share/applications/idle.desktop

Add a %f to the end of the line, save - like

Exec=/usr/bin/idle -n %f

Then ck. again & see if Idle is now the default, do a log out/in if needed. Once it's added then you can reopen idle.desktop & remove the %f, it should stay as default. I'm not sure if %f is appropriate for idle, otherwise I'd say you could leave it

Here's how you do it:

1. Go to a folder that contains a Python file.
2. Right-click on any Python file.
3. Select Properties.
4. Next to the section that says “Opens with”, click the Change button.
5. You may need to select More Options.
6. Click on Look for another app on this PC.
7. Navigate to where you installed Python. For me, that’s the Python34 folder on the C drive.
8. Open Lib
9. Open idlelib
10. Select the idle.bat file.
11. Click Open.
12. Click OK to close out of Properties.
13. Now you can open .py files in IDLE simply by double-clicking on them.

We also have a video showing how to associate Python files with IDLE.