class MainMenu(tk.Frame):

def __init__(self, parent, controller):
    tk.Frame.__init__(self, parent)
    self.controller = controller
    label = tk.Label(self, text="     Main Menu - Login    ", fg="red", font=controller.title_font2)
    label.pack(side="top", fill="x", pady=20)
    usernameL = tk.Label(self, text="Username").pack(side="top")
    uUserLogin = tk.Entry(self)
    uUserLogin.pack()
    passwordL = tk.Label(self, text="Password").pack(side="top")
    uUserPassword = tk.Entry(self)
    uUserPassword.pack()

    def checkUser():
        uLoginUser = False
        uLoginPassword = False
        uUserCheck = uUserLogin.get()
        uUserCheckP = uUserPassword.get()
        with open("Users.csv", "r") as f:
            csvreader = csv.reader(f, delimiter=",")
            for row in csvreader:
                if uUserCheck == row[0]:
                    uLoginUser == True
                    if uUserCheckP == row[1]:
                        uLoginPassword == True
                        #labelT = tk.Label(self, text="Hello")
                        #labelT.pack()
        if uLoginUser and uLoginPassword == True:
            controller.show_frame("MainTMenu")

    submit = tk.Button(self, text="Submit",
                       command=checkUser())
    submit.pack()


    #If correct -> Go to next frame

Users, Passwords
 user, password
 user, password