У меня есть проблема с кодом на Python, я не знаю, что делать ? пожалуйста, помогите мне

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проблема кода me заключается в том, что кнопка не работает над этим кодом

Что я уже пробовал:

<pre>from tkinter import *
import tkinter.messagebox as tkMessageBox
import mysql.connector
root = Tk()
root.title("login software")
 # ================= Setting up the Main Frame =================
width = 640
height = 480
screen_width = root.winfo_screenwidth()
screen_height = root.winfo_screenheight()
x = (screen_width/2) - (width/2)
y = (screen_height/2) - (height/2)
root.geometry("%dx%d+%d+%d" % (width, height, x, y))
root.resizable(0, 0)
     # ================= Designing the Layout ===================== 
Top = Frame(root, bd=2,  relief=RIDGE)
Top.pack(side=TOP, fill=X)
Form = Frame(root, height=200)
Form.pack(side=TOP, pady=20)
#==============================VARIABLES======================================

USERNAME = StringVar()
PASSWORD = StringVar()
 # ================= Designing the Layout =================
lbl_title = Label(Top, text = "Python: Simple Login Application", font=('arial', 15)).pack(fill=X)
lbl_username = Label(Form, text = "Username:", font=('arial', 14), bd=15).grid(row=0, sticky="e")
lbl_password = Label(Form, text = "Password:", font=('arial', 14), bd=15).grid(row=1, sticky="e")
lbl_text = Label(Form).grid(row=2, columnspan=2)
username = Entry(Form, textvariable=USERNAME, font=(14)).grid(row=0, column=1)
password = Entry(Form, textvariable=PASSWORD, show="*",font=(14)).grid(row=1, column=1)
b = Button(Form, text="OK", command= login ).pack()
#========================================INITIALIZATION===================================
root.mainloop()

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