[Tkinter] Sudoku solver with tkinter

[flash77]

Hello,
I changed the complexity of the example to concentrate on the basics.

The function SquareCreate() generates the squares.

I'm trying to read in the values of the entries with the function readin().

In line 24 it is mentioned that "list index ist out of range".

What I am doing wrong?

I ask politely for help...

Greetings, flash77

import tkinter as tk
from tkinter import Entry, IntVar, Tk

def quit_frame():
    main.destroy()

def SquareCreate(): 
    sq=[]
    for j in range(1,4):
        for i in range(1,4):
            data = IntVar()
            t = tk.Entry(main, textvariable=data, justify="center",font=("Arial",16))
            t.place(x=i*40, y=j*40, width=40, height=40)
            t.delete(0)
            sq.append(data)
    return sq

def readin():
    sq=[]
    bo=[]
    for r in range(1,4):
        row=[]
        for c in range(1,4):
            row.append(sq[r*9+c].get())
        bo.append(row)    
    return bo 
            
#mainprogramm
main = tk.Tk()
main.geometry("500x540")
main.resizable(width=0, height=0)
l=tk.Label(main, text="Sudoku Bruteforce Solver")
l["font"]="Arial"
l.place(x=150,y=0)
button1=tk.Button(main, text="quit", command = quit_frame)
button1.place(x=50,y=450)
button2=tk.Button(main, text="readin", command = readin)
button2.place(x=150,y=450)
SquareCreate()
main.mainloop()