Why is the program not running? Is there a logical or syntax problem?

[behi00]

thanks for your helps but not run yet?
why??!! i don't know.

import tkinter as tk

class Profit:
    def __init__(self, master):
        self.master = master
        master.title("Profit")
        # create the  pro field
        self.pro_label = tk.Label(master, text= "Interest rate:")
        self.pro_label.grid(row=0, column=0)
        # create the display
        self.display = tk.Entry(master, width=10, justify="center", font=("Arial", 10))
        self.display.grid(row=0, column=1)
        # create the  result field
        self.res_label = tk.Label(master, text="Result:")
        self.res_label.grid(row=1, column=0)
        # create and place the buttons on the grid
        self.calculate_button = tk.Button(master,text="Computing",command=self.calculate)
        self.calculate_button.grid(row=2, column=0)

    def rule(master):
          return 72/master

    def calculate(self):
        x = int(self.display.get())
        result = "Result:   " + self.rule()
        self.res_label.config(text=result)
        # create the main window and profit object
        root = tk.Tk()
        pro = Profit(root)
        root.mainloop()