When attempting to edit a script tool in ArcGIS Pro, the underlying Python script opens in Notepad instead of IDLE.

Workaround

Set the Script Editor in ArcGIS Pro to the 'idle.py' file within the active Python environment. The workflow to do this is referenced below:

1. Go to ArcGIS Pro's Settings pane, which is accessed by either clicking the Project tab inside of an ArcGIS Pro project or clicking the Settings side tab in ArcGIS Pro's home page.
2. In the list of side tabs, click Options. 
3. In the Options dialog box, click the Geoprocessing side tab.
4. Next to the Script Editor setting, click the 'Browse..' button (which looks like an open file) to open the 'Select your script editor' dialog box.
5. In the 'Select your script editor' dialog box, navigate to the location of the 'idle.py' file in the active Python environment, select that 'idle.py' file, and click OK.
6. In the Options dialog box, click OK to apply the Script Editor change and close the Options dialog box.

Steps to Reproduce