Tkinter window not opening, but if I comment out a line, it works

So I was trying to create a GUI in pygame, but after a while, I just decided to re-write it in tkinter. I need to create 3 bars, one being a canvas, the other 2 being empty. The size of the left bar is leftbarwidth and the right rightbarwidth, set to 200 and 300 respectively. So far I have this (The logic of the program not included)

 1 from tkinter import *
 2 
 3 def windowsizeupdate(event):
 4     preview.config(width=event.width-leftbarwidth-rightbarwidth, height=event.height)
 5 
 6 root = Tk()
 7 root.title("TITLE HERE")
 8 root.geometry(f"{leftbarwidth + rightbarwidth + 200}x600+{int(screen.winfo_screenwidth() / 2 - (leftbarwidth + rightbarwidth + 200) / 2)}+{int(screen.winfo_screenheight() / 2 - 300)}")
 9 root.minsize(800, 600)
10 root.attributes("-topmost", 1)
11
12 preview = Canvas(root, bd=0, bg="#800000", cursor="dot", width=200, height=600)
13 preview.place(x=leftbarwidth, y=0)
14
15 root.bind("<Configure>",windowsizeupdate)
16 root.mainloop()

But whenever I run it, I just get this:

After commenting out line 4, and replacing it with print(event.width-leftbarwidth-rightbarwidth, event.height, leftbarwidth), I discovered
everything works, and all the values should work with the config function!

But if I put in this:

 1 from tkinter import *
 2 
 3 def windowsizeupdate(event):
 4     print(event.width-leftbarwidth-rightbarwidth, event.height, leftbarwidth)
 5     preview.config(width=event.width-leftbarwidth-rightbarwidth, height=event.height)
 6 
 7 root = Tk()
 8 root.title("TITLE HERE")
 9 root.geometry(f"{leftbarwidth + rightbarwidth + 200}x600+{int(screen.winfo_screenwidth() / 2 - (leftbarwidth + rightbarwidth + 200) / 2)}+{int(screen.winfo_screenheight() / 2 - 300)}")
10 root.minsize(800, 600)
11 root.attributes("-topmost", 1)
12
13 preview = Canvas(root, bd=0, bg="#800000", cursor="dot", width=200, height=600)
14 preview.place(x=leftbarwidth, y=0)
15
16 root.bind("<Configure>",windowsizeupdate)
17 root.mainloop()

I see my console output looks like this:

Can someone explain this to me!

>Solution :

Because when you resize the window, that raises another <Configure> event and recalls your handler. You need to detect that the event wat not triggered by your change:

def windowsizeupdate(event):
     if event.x != leftbarwidth:
        preview.config(width=event.width-leftbarwidth-rightbarwidth, 
height=event.height)