Бял екран когато стартирам приложението Суматор на числа от основи на програмирането с Python

Здравейте, написах кода от книгата, но когато стратирам приложението няма никакви бутони или полета, само бял бекграунд. Това е кодът ми:

import tkinter as tk


class Application(tk.Frame):
    def __init__(self, master=None):
        super().__init__(master)

        self.pack()


# create the application
app = Application()
app.master.title("Sumator")
app.master.minsize(width=300, height=150)

# start the program
app.mainloop()


def __init(self, master=None):
    super().__init__(master)

    self.pack()
    self.create_widgets()


def create_widgets(self):
    # create widgets
    self.firstNumberEntry = tk.Entry()
    self.plusSign = tk.Label(text="+")
    self.secondNumberEntry = tk.Entry()
    self.equalSign = tk.Label(text="=")
    self.resultLabel = tk.Label(text="Result...",
                                bg="blue", fg="white")
    self.calculateButton = tk.Button(text="Calculate")
    # place widgets
    self.firstNumberEntry.pack(side="left")
    self.plusSign.pack(side="left")
    self.secondNumberEntry.pack(side="left")
    self.equalSign.pack(side="left")
    self.resultLabel.pack(side="left")
    self.calculateButton.pack(side="left")

А това е резултатът:

Някой има ли идеи къде е проблемът?

import tkinter as tk class Application(tk.Frame): def __init__(self, master=None): super().__init__(master) self.pack() self.create_widgets() def create_widgets(self): # create widgets self.firstNumberEntry = tk.Entry() self.plusSign = tk.Label(text="+") self.secondNumberEntry = tk.Entry() self.equalSign = tk.Label(text="=") self.resultLabel = tk.Label(text="Result...",bg="blue", fg="white") self.calculateButton = tk.Button(text="Calculate") # place widgets self.firstNumberEntry.pack(side="left") self.plusSign.pack(side="left") self.secondNumberEntry.pack(side="left") self.equalSign.pack(side="left") self.resultLabel.pack(side="left") self.calculateButton.pack(side="left") # create the application app = Application() app.master.title("Sumator") app.master.minsize(width=300, height=150) # start the program app.mainloop()