MainWindow.changepage() missing 1 required positional argument: 'self'

Question

I'm trying to program a small login window, but I seem to be stuck on my understanding of classes, functions and attributes. it keeps giving me an error saying MainWindow.changepage() missing 1 required positional argument: 'self'.

My code is also a bit unorganized because I'm just moving stuff around hoping to understand and fix it.

import customtkinter as tk 

class Login(tk.CTkFrame):
     def __init__(self, parent):
        super().__init__(parent)

        global username
        global password

        username = tk.CTkEntry(self, justify="center", placeholder_text="username", width=200)
        username.pack(pady=20)

        password = tk.CTkEntry(self, justify="center", placeholder_text="password", width=200)
        password.pack()


        button = tk.CTkButton(self, text="Login", command=Check.check_user)
        button.pack(pady=20)

        self.pack(padx=10, pady=10)

class Check():
     def check_user():
        user = username.get()
        passw = password.get()

        if user in users and passw == users[user]:
                print("welcome " + user)
                main = MainWindow
                main.changepage()

        else:
                print("incorrect username or password")

class SecondWindow(tk.CTkFrame):
     def __init__(self, parent):
          super().__init__(parent)
          tk.CTkLabel(self, text="Welcome to jadajada").pack(pady=10,padx=10)
          self.pack(padx = 10, pady=10)

class MainWindow():
     def __init__(self, master):
        mainframe = tk.CTkFrame(master)
        mainframe.pack(padx= 10, pady= 10, fill= "both", expand = True)

        self.index = 0

        self.framelist = [Login(mainframe), SecondWindow(mainframe)]
        self.framelist[1].forget()
     
     def changepage(self):
        self.framelist[self.index].forget()
        self.index = 1
        self.framelist[self.index].tkraise()
        self.framelist[self.index].pack(pady=10,padx=10)

#details
users = dict(namviper="luapnam23", paul="grellmann", luap="nam")

#main window
root = tk.CTk()
root.geometry("500x500")
root.title("Login System")
tk.set_appearance_mode("dark")
tk.set_default_color_theme("green")

#main systems
window = MainWindow(root)

#mainloops
root.mainloop()

Answer 1

Your error is here:

class Check():
     def check_user():
        user = username.get()
        passw = password.get()

        if user in users and passw == users[user]:
                print("welcome " + user)
                main = MainWindow # error here
                main.changepage()

        else:
                print("incorrect username or password")

I'm pretty sure you meant to instantiate (create an instance of a class). For this you need to add parentheses after MainWindow and pass the proper parameters such that the line becomes MainWindow(root). You may need to rework your code so that you can pass the correct parameter. An alternative would be to pass the MainWindow object (main) itself to Check.check_user.

Other note, your Check class is useless as it stores no data and only has one function. This could simply be a function.