import tkinter as tk


class Application(tk.Frame):

    def __init__(self, master=None):  # Моля за обяснение, защо self не е повече метод, а променлива? Къде бъркам?
        super().__init__(master)

        self.pack()
        self.create_widgets()

    def create_widgets(self):
        # create widgets
        self.firstNumberEntry = tk.Entry()
        self.plusSigh = tk.Label(text="+")
        self.secondNumberEntry = tk.Entry()
        self.equalSign = tk.Label(text="=")
        self.resultLabel = tk.Label(text="Result...", bg="green", fg="white")
        self.calculateButton = tk.Button(text="Calculate")

        # place widgets
        self.firstNumberEntry.pack(side="left")
        self.plusSigh.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=100, height=50)

# start the program
app.mainloop()