There are 3 ways to scroll by key in each direction: Arrow Down/Up, Page Down/Up, and Cntl End/Home.  There are 4 ways to scroll by mouse, in each direction: Mousewheel down/up, Scrollbar arrow bottom/top (== Arrow keys), Scrollbar trough below/above slider (= Page keys), and Scrollbar slider.

On Windows, if I Load Module idlelib.editor and go to the bottom, with the text cursor on the last line, all up methods work.  Bruce, which of the four mouse up methods don't work for you?  Just grabbing the slider, as Ned found?  What happens is you move the slider down, and try to move up without releasing the button?

Cheryl or Tal, can one of you check on Linux?

In the text area, the mouse pointer, for me, is a vertical bar and the slider is a light gray.  When I move the mouse over the scrollbar slider, the slider become active and ready to click on.  The indication is that the mouse pointer becomes an arrow pointing up left and the slider turns dark gray.  When the mouse is over the scrollbar trough or arrows, the slider only darkens to medium gray.  When over an arrow, the arrow darkens. Bruce, do you see the 'activation' change when the slider is at the bottom and you mouse over it, but cannot grab it?


In May, we changed the 3.6+ editor text/mousewheel/scrollbar interaction a bit so that the text scrolled by lines, rather than by pixel. #33664, PR 7351. There is always a complete line at the top -- unless one changes the window height to a non-integral number of lines and moves the cursor to the last line.  (Then the complete lines are at the bottom until one moves the cursor to the top line  -- Cheryl, we should try to fix this.)

The patch changed the command function that the scrollbar calls when it is clicked or the slider is moved to editor.EditorWindow.handle_yview. The new function has an extraneous "return 'break'" that can and should be removed.  But I doubt that is the problem.  It also has new code that is only executed for slider movements.

If only the slider has a problem and this slider code were to raise when at the bottom, we might have an explanation.  I am dubious, as the only possible platform-specific calls are the tkinter calls text.index('end') and text.index('@0.0').  To check this anyway, please start IDLE in the Mac terminal with 'python3 -m idlelib'  (correct on Mac?) and repeat the failing action and see if a traceback appears.

It might also help to know if 2.7 or 3.5- have the same problem.