#Imoprt Tkinter module
import tkinter as tk

#F to set grid and button
def set_grid():
    for x in range(9):
        for y in range(9):
            cell = tk.Entry(window, width = 2)
            cell.grid(row = x, column = y)
            sudoku[x].append(cell)
    solve_but = tk.Button(window, text = "Solve", command = solve_sudoku)
    solve_but.grid(row = 0, column = 9)

#F to find empty cell
def find_empty():
    for x in range(9):
        for y in range(9):
            if sudoku[x][y].get() == "":
                return (x, y)
    return False

#F to get if num in col
def num_in_col(y, num):
    for x in range(9):
        if sudoku[x][y].get() == str(num):
            return True
    return False

#F to get if num in row
def num_in_row(x, num):
    for y in range(9):
        if sudoku[x][y].get() == str(num):
            return True
    return False

#F to get if num in box
def num_in_box(xbox, ybox, num):
    for x in range(3):
        for y in range(3):
            if sudoku[x + xbox][y + ybox].get() == str(num):
                return True
    return False

#F to validate cell
def validate_cell(x, y, num):
    return not (num_in_row(x, num)) and not (num_in_col(y, num)) and not (num_in_box(x - (x % 3), y - (y % 3), num))

#F to solve puzzle
def solve_sudoku():
    find = find_empty()
    if not find_empty():
        return True
    else:
        x, y = find
    for num in range(1, 10):
        if validate_cell(x, y, num):
            sudoku[x][y].delete(0, "end")
            sudoku[x][y].insert(0, str(num))
            sudoku[x][y].config(fg = "SpringGreen3")
            #==> here goes the delay <==
            if solve_sudoku():
                return True
            sudoku[x][y].delete(0, "end")
    return False

#----------------- Main -----------------
if __name__ == "__main__":
    # Set window
    window = tk.Tk()

    # Set sudoku
    sudoku = [[] for _ in range(9)]

    # Set GUIs grid
    set_grid()

    # Keep the app running
    window.mainloop()