MacOS Sierra 10.12.6, Python 3.6.1, tk 8.5.15 or .18.  Consider this code with arbitrary compound statements and therefore indented lines.

for i in range(10):
    if i%2:
        print(f(i))

Irv Kalb on idle-dev thread 'Bug in cursor placement in IDLE editor' windows reports the following obnoxious behavior: click just to left or on left side of 'p' and cursor appears on left margin.  Keep clicking and cursor moves right one space at a time until arriving next to 'p', where it should immediately go, and does on Windows, and, I presume, elsewhere.  (When the cursor first arrives at 'p', there is also the double-click selection highlight.)

At my suggestion, he also tested with code inserted directly in a tk Test window with this:

import tkinter as tk
root = tk.Tk()
text = tk.Text(root)
sample = '''
<replace this with sample that allows reported error>
'''
text.insert('1.0', sample)
text.pack()
root.mainloop()

and encountered the same bug.  (Hence, this is not an IDLE issue.)The only difference is that clicking beside keyword 'if' does not show bug in IDLE but does in Text.  He also uploaded an unlisted video to YouTube.
https://www.youtube.com/watch?v=Us8px0BY5rg

Irv's current workaround is to click a letter or two to the right and use <-- key.

I realize that this is likely not a tkinter issue either, but I wanted to record it and get you two's thoughts.  Is this more likely to be a problem with a particular installation, or with at least one macOS release and even 8.5.18.

If the latter, can Irv install Python compiled elsewhere to work with 8.6?  Ned, do you have a recommendation?

Kevin Walzer reported that he does not see the issue with Python built to run with 8.6 and using 8.6.7.  He noted that 8.5.18 does not get bug fixes.  I presume that this applies to 8.5 in general.  Will 3.7.0 be compiled for 8.6?