Since I've started using IDLE to program in Python, I have always wanted IDLE to have a horizontal scrollbar. But only recently I have figured out how to do this.
In this example, we will add a horizontal scrollbar.
First, go to your Python folder. Mine is here: C:UsersMSI_PCAppDataLocalProgramsPythonPython36
Then, go to Lib/idlelib.
Open up editor.py You may want to backup this file just in case.