import tkinter as tk

window = tk.Tk()

frame1 = tk.Frame(master=None, width=200, height=100, bg="red")
frame1.pack(fill=tk.BOTH, side=tk.TOP, expand=False)

frame2 = tk.Frame(master=None, width=100, height=50, bg="yellow")
frame2.pack(fill=tk.BOTH, side=tk.TOP, expand=False)

frame3 = tk.Frame(master=None, width=50, height=25, bg="blue")
frame3.pack(fill=tk.BOTH, side=tk.TOP, expand=False)

window.mainloop()

fill and side interactions

Problem is I expect tk.BOTH to fill vertically when I drag window down, but it does not (seen by grey background of window). It only fills horizontally.

When i change all 3 frames’ sides from tk.TOP to tk.LEFT, it fills vertically but not horizontally

Based on above 2 experiments, is it true side value changes behavior of fill=tk.BOTH, making it work only in 1 direction each time?

To further test, with side=tk.LEFT, I changed tk.BOTH in all frames to tk.Y, then tk.X.
tk.Y behaves the same as tk.BOTH. tk.X still does not fill horizontally, but now also does not fill vertically (as expected)

fill and expand interactions

If I set all 3 frames expand = True, all the previously failed fills are now successfully filling.
I’m confused did the fill=tk.BOTH now work because of expand=True, or tk.BOTH still does not work, and expand took over the role of filling for the failed direction?

If the latter, what’s the purpose of tk.BOTH since it always fails to fill in 1 direction depending on side, and depends on expand=True to make up for it’s failures?