視窗形式 驗證是否輸入為四位數

import tkinter as tk
import tkinter.messagebox as tmsg
import random

def ButtonClick():
    #a=[random.randint(1,9),random.randint(1,9),random.randint(1,9),random.randint(1,9),]
    b=editbox_1.get()
   
    if (len(b)!=4):
        tmsg.showerror("錯誤","請重新輸入")
    else:
        kazuok=True
        for i in range(4):
            if (b[i]>"9" or b[i]<"0"):
                tmsg.showerror("錯誤","請重新輸入")
                kazuok=False
                break
        if kazuok:
            tmsg.showinfo("你輸入的文字",b)
root=tk.Tk()
root.title("猜數字遊戲")
root.geometry("400x200")
label_1=tk.Label(root,text="請輸入數字",font=("Helvetica",14))
label_1.place(x=20,y=20)

editbox_1=tk.Entry(width=4,font=("Helvetica",14))
editbox_1.place(x=150,y=20)

button_1=tk.Button(root,text="確認",font=("Helvetica",14),command=ButtonClick)
button_1.place(x=150,y=60)

root.mainloop()