Correct way to set scrollbar position in python tkinter

Question

I am making a basic text editor and I am saving the scroll position in a file on closing the program. Then when opening the program it will read the scroll position from the file and update it so you can continue where you left off.

I can get the position fine from scrolledtext.yview() which returns a tuple with e.g. (0.42, 0.75)

But I cannot figure out how to change the scroll position. I have tried scrolledtext.vbar.set(0.42, 0.75) to try and update it but that doesn't work as in it doesn't do anything and gives no errors. I have also tried scrolledtext.yview(0.42, 0.75) but it says TclError: bad option "0.42": must be moveto or scroll so if anyone knows how to update it that would be greatly appreciated, cheers.

Edit(Code):

import tkinter as tk root = tk.Tk() Frame = frame(root) Frame.pack() textbox = ScrolledText(Frame) textbox.pack() textbox.yview() #this is saved to file, produces tuple of e.g. (0.42, 0.75) textbox.vbar.set(0.3, 0.7) #this doesn't produce any errors but doesn't change the scroll position textbox.yview(0.3, 0.7) #this is also something i have tried but produces the error _tkinter.TclError: bad option "0.4243827160493827": must be moveto or scroll root.mainloop()

If you could please provide a code example of what you have tried we can better assist. Please provide Minimal, Complete, and Verifiable example. — Mike - SMT
– Mike - SMT, Commented Nov 5, 2018 at 16:26

Bryan Oakley · Accepted Answer · 2018-11-05 16:41:06Z

You can't expect the saved yview to work in all cases. If the file has been edited, the proportions could be all wrong.

The tuple you get from yview represents the fraction visible at the top and the fraction visible at the bottom. You can call yview_moveto to set the position at the top, and then let tkinter take care of the fraction at the bottom.

For example, if the yview you've saved is (0.42, 0.75), then you just need to call yview_moveto('0.42'). This will cause the view to be adjusted so that the given offset is at the top of the window.

Thank you! It saves the last yview before closing the program so it should always open back up the correct position, right? Also, is there any chance you have a link to a page explaining this in more detail?
@JohnT: there's no document that explains this in more detail. However,several tkinter documentation sites mention the yview_moveto command and its arguments.

Valeriy Chepelev · Accepted Answer · 2021-03-10 13:01:54Z

In case of widgets update with change bbox sizes, i use a followed snippet to keep scroll position:

#before repaint store vsb position caclulated in pixels from top bbox = canvas.bbox(ALL) self.mem_vsb_pos = canvas.yview()[0] * (bbox[3] - bbox[1]) #after repaint (back calculation): bbox = canvas.bbox(ALL) canvas.yview_moveto(self.do_vsb_pos / (bbox[3]-bbox[1])) #before repaint - if need repaint from top self.mem_vsb_pos = 0.0

@Valeriy Chepelev What does bbox[3]-bbox(https://stackoverflow.com/users/15368340/valeriy-chepelev) mean? Why can't just bbox[3] be used?
@АлександрМ , at "before repaint" we store relative scroll position, so on "after repaint" we recalculate position for a new bbox size.

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