我必须在tkinter中为我的学校项目做一个CRUD应用程序。到目前为止，我已经注册并登录了。现在我想从user.py中的类User中的类main.py中的类App中获取变量user_data。在“用户”窗口中显示用户数据。
main.py

from tkinter import *
from tkinter.messagebox import showerror
import sqlite3

db = sqlite3.connect("wypożyczalnia_aut.db")
cursor = db.cursor()

class App(Tk):
    def __init__(self):
        super().__init__()
        self.title("Zaloguj Się")
        self.geometry("300x400")

        login_font = ("Comic Sans MS", 20, "bold")

        Label(self, text="Zaloguj Się", font=login_font).pack(padx=10, pady=10)

        self.username = Entry(self)
        self.password = Entry(self, show="*")
        self.username.pack(padx=10, pady=10)
        self.password.pack(padx=10, pady=10)

        self.login_btn = Button(self,text="Zaloguj Się", command=self.login).pack(padx=10, pady=10)
        self.sign_up_btn = Button(self,text="Zarejestruj Się", command=self.open_window_sign_up).pack(padx=10, pady=10)

    def open_window_sign_up(self):
        from sign_up import SignUp
        sign_up_window = SignUp(self)
        sign_up_window.grab_set()
    
    def login(self):
        from user import User
        cursor.execute("SELECT * FROM uzytkownicy WHERE nazwa=? AND haslo=?", (self.username.get(), self.password.get()))
        global user_data
        user_data = cursor.fetchone()
        if user_data is not None:
            user_window = User(self)
            user_window.grab_set()
        else:
            showerror(title='Błąd',message='Niepoprawna Nazwa/Hasło')

        

if __name__ == "__main__":
    app = App()
    app.mainloop()

db.commit()
db.close()

user.py

from tkinter import *
import sqlite3
import main

class User(Toplevel):
    def __init__(self,parent):
        super().__init__(parent)
        self.geometry("1280x720")
        self.title("Panel Użytkownika")

        self.data = main.user_data

我得到错误：AttributeError: module 'main' has no attribute 'user_data'