import a python file that create a window when main window button clicks

Question

I am creating 2 window in my program and i am using two class, since the code is complex, i separate it in 2 different python file. After i imported the second window file, how can i make sure it open without having this error which show in this picture

The original result should look like this after the new window button clicked:

Coding for Main Window:

from tkinter import *
import classGUIProgram
class Window(Tk):
    def __init__(self, parent):
        Tk.__init__(self, parent)
        self.parent = parent
        self.initialize()

    def initialize(self):
        self.geometry("600x400+30+30")
        self.wButton = Button(self, text='newWindow', command =     self.OnButtonClick)
        self.wButton.pack()

    def OnButtonClick(classGUIProgram):
        classGUIProgram.top = Toplevel()
        master = Tk()
        b = classGUIProgram.HappyButton(master)
        master.mainloop()
if __name__ == "__main__":
    window = Window(None)

    window.title("title")

    window.mainloop()

Coding for Second Window:

from tkinter import *
class HappyButton:
    def __init__(self, master):
        frame = Frame(master)
        frame.pack()
        self.printButton = Button(frame, text="Print message", command=self.printMessage)
        self.printButton.pack(side=LEFT)

        self.quitButton = Button(frame, text="Quit", command= quit)
        self.quitButton.pack(side=LEFT)

        self.downloadHistoryCB=Checkbutton(frame, text="Download History")
        self.downloadHistoryCB.pack(side=LEFT)

    def printMessage(self):
        print("Wow this actually worked!")

master = Tk()
b = HappyButton(master)
master.mainloop()

Answer 1

You're creating extra Tk windows. Here is an example of using Toplevel widgets and another file.

mainWindow.py

import tkinter as tk
import secondWindow as sW

class MainWindow(tk.Tk):
    def __init__(self):
        super().__init__()
        self.title("Main Window")
        self.geometry("600x400+30+30")

        tk.Button(self, text = "New Window", command = self.new_window).pack()
        tk.Button(self, text = "Close Window", command = self.close).pack()

        self._second_window = None

    def new_window(self):
        # This prevents multiple clicks opening multiple windows
        if self._second_window is not None:
            return

        self._second_window = sW.SubWindow(self)

    def close(self):
        # Destory the 2nd window and reset the value to None
        if self._second_window is not None:
            self._second_window.destroy()
            self._second_window = None


if __name__ == '__main__':
    window = MainWindow()
    window.mainloop()

secondWindow.py

import tkinter as tk

class SubWindow(tk.Toplevel):
    def __init__(self, master):
        super().__init__(master)

        self.title("Sub Window")
        self.geometry("400x300+30+30")
        # Change what happens when you click the X button
        # This is done so changes also reflect in the main window class
        self.protocol('WM_DELETE_WINDOW', master.close)

        tk.Button(self, text = "Print", command = self.printMessage).pack()

    def printMessage(self):
        print("Wow this actually worked!")

When using another file be sure to not have any global code you don't want running. Your classes don't have to inherit from Tk and Toplevel, this is just an example. But you need to ensure you only ever have one instance of Tk otherwise you get the behaviour you encountered