TypeTrainer OOP Tkinter program [closed]

Question

I've been developing my first real python gui-program for a while now. Having watched some tutorials to tkinter and OOP I've gotten quite far, but now I just can't get my code to do what I want it to.

So here's my code so far:

import random
import string
import time
import datetime
import tkinter as tk
import pandas as pd

# GUI

# Define text variabels:
intro_txt = "Welcome to Typetrainer!\n This program will help you get faster at typing on your PC"

instr_txt = "Instructions:\n-Place your right index finger on the letter J, your left index finger on F" \
         "\n-Type the string you see as fast as you can using all ten fingers" \
         "\n-Don't look at the keyboard !"

diff_txt = "Please select a difficulty"

go_txt = "Type the above string as fast as you can and hit enter !"

# Create custom fontvariables

NORMAL_FONT=("Verdana", 12)
LARGE_FONT=("Verdana", 18)

# Define difficulties

diff_levels = {"Easy": 5, "Medium": 10, "Hard": 15, "Expert": 20}

class TypeTrainerGUI(tk.Tk):
    def __init__(self, *args, **kwargs):  # initialize the TypeTrainerGUI class; 
        # *args: generally used for all the arguments, **kwargs: passing through dictionaries
        tk.Tk.__init__(self, *args, **kwargs)  # initialize Tkinter within the TypeTrainerGUI class
        container = tk.Frame(self)

        container.pack(side="top", fill="both", expand=True)

        container.grid_rowconfigure(0, weight=1)
        container.grid_columnconfigure(0, weight=1)

        self.frames = {}  # this holds all the different "windows" that the GUI can show and the user can interact with

        for F in (StartPage, DifficultySelection, TypePage):  # "activates" the frames so that 
            # they can be cycled through

            frame = F(container, self)

            self.frames[F] = frame

            frame.grid(row=0, column=0, sticky="nsew")  # .grid defines where the frame sits; sticky defines 
            # alignment and strech

        self.title("Type Trainer")

        self.show_frame(StartPage)

    def show_frame(self, cont):  # define the .show_page method; moves a frame to the top so 
        # the user can interact with it

        frame = self.frames[cont]
        frame.tkraise()

    def init_game(self, diff_in):  # set the parameters for the game to run with

        global cnt
        global score

        print(diff_in) # check if the correct value is passed

        # Define a object that creates a lowercase letter string of length a

        self.question_txt = ''.join(random.choice(string.ascii_lowercase) for x in range(diff_in))

        print(self.question_txt) # check if correct text is generated

        cnt = 0  # Counter for the no of rounds
        score = 0  # Track the score

class StartPage(tk.Frame):  # Create start page

    def __init__(self, parent, controller):  # initialize the frame
        tk.Frame.__init__(self, parent)  # initialize tkinter
        label = tk.Label(self, text=intro_txt, font=LARGE_FONT)  # create label
        label_2 = tk.Label(self, text=instr_txt, font=NORMAL_FONT)  # create label

        label.pack(pady=10, padx=10)
        label_2.pack(pady=10, padx=10)

        next = tk.Button(self, text="Next", command=lambda: controller.show_frame(DifficultySelection))
        next.pack()

class DifficultySelection(tk.Frame):  # Create difficulty selection page

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        label = tk.Label(self, text=diff_txt, font=NORMAL_FONT, justify=tk.LEFT)
        label.pack(pady=10, padx=10)

        self.choice = tk.IntVar()

        for (diff, val) in diff_levels.items():
            tk.Radiobutton(self, text=diff, padx=20, variable=self.choice, value=val,
                           command=lambda: controller.init_game(self.choice.get())).pack(anchor=tk.W)

        start = tk.Button(self, text="Start game", command=lambda: controller.show_frame(TypePage))
        start.pack()


class TypePage(tk.Frame):  # Create the interaction page

    def __init__(self, parent, init_game):

        tk.Frame.__init__(self, parent)
        label = tk.Label(self, text=go_txt, font=NORMAL_FONT)
        label.pack(pady=10, padx=10)

        question = tk.Label(self, text=question_txt, font=NORMAL_FONT)
        question.pack(pady=10, padx=10)

        usr_input = tk.Entry(self)
        usr_input.pack(pady=10, padx=10)
        usr_input.focus_set()

gui = TypeTrainerGUI()
gui.mainloop()

Ok, so what I want to do is get the value that's selected by clicking a radiobutton and pass it to init_game to create question_txt (and other stuff but I'm leaving that out for now). To do this I use this part of code

self.choice = tk.IntVar()

            for (diff, val) in diff_levels.items():
                tk.Radiobutton(self, text=diff, padx=20, variable=self.choice, value=val,
                               command=lambda: controller.init_game(self.choice.get())).pack(anchor=tk.W)

This all works just fine. init_game does what I want it to do (checked with print(diff_in) and print(question_txt)). Now I want to use question_txt in the TypePage class as text for the question label.

question = tk.Label(self, text=question_txt, font=NORMAL_FONT)
        question.pack(pady=10, padx=10)

Doing this throws a name error: "name 'question_txt' is not defined". I just don't get how I can use question_txt in a different class. I tried to make it a global variable, but that also didn't solve the problem.

I would really appreciate any help with this. Thanks !

N.B.: Since this is my first try at OOP AND tkinter please be leneant. Though all comments on how to write better/more understanbale code are greatly appreciated !