Make stretchable split screen in Tkinter

The main problem with your code is that you're not using PanedWidnow correctly. For example, you can't pack or grid one PanedWindow inside another. To place one widget inside a PanedWindow you must use the paned window .add() method. So, to put m2 inside m1 you must do m1.add(m2). Treat a PanedWindow like a Frame, and .add() is the equivalent to .pack() or .grid().

Also, it seems like you're thinking an PanedWindow is a pane, which it is not. If you want three panes for three side-by-side windows, you only need to create a single instance of PanedWindow, and then call .add(...) three times, once for each child window. While you can put paned windows inside paned windows, it's rarely the right thing to do unless one is horizontal and the other is vertical. For most circumstances, a single instance of PanedWindow is all you need.

You're making this way too complicated. Just following the first example here, I made what you want:

from Tkinter import *root = Tk()m = PanedWindow(root)m.pack(fill=BOTH, expand=1)text1 = Text(m, height=15, width =15)m.add(text1) text2=Text(m, height=15, width=15)m.add(text2) root.mainloop()