Miles Per Gallon Calculator

import tkinter

class MPG:
    def __init__(self):
        self.main_window = tkinter.Tk()

        self.gallons_frame = tkinter.Frame(self.main_window)
        self.miles_frame = tkinter.Frame(self.main_window)
        self.mpg_frame = tkinter.Frame(self.main_window)
        self.button_frame = tkinter.Frame(self.main_window)


        self.gallons_label = tkinter.Label(self.gallons_frame,
                                        text='Enter the number of gallons: ')
        self.gallons_entry = tkinter.Entry(self.gallons_frame,
                                         width=10)
        self.gallons_label.pack(side='left')
        self.gallons_entry.pack(side='left')


        self.miles_label = tkinter.Label(self.miles_frame,
                                           text='Enter the number of miles: ')
        self.miles_entry = tkinter.Entry(self.miles_frame,
                                           width=10)
        self.miles_label.pack(side='left')
        self.miles_entry.pack(side='left')


        self.result_label = tkinter.Label(self.mpg_frame,
                                       text='Miles Per Gallon')
        self.mpg = tkinter.StringVar()
        self.mpg_label = tkinter.Label(self.mpg_frame,
                                       textvariable=self.mpg)
        self.result_label.pack(side='left')
        self.mpg_label.pack(side='left')


        self.calc_button = tkinter.Button(self.button_frame,
                                          text='Calculate MPG',
                                          command=self.calc_mpg)
        self.quit_button = tkinter.Button(self.button_frame,
                                          text='Quit',
                                          command=self.main_window.destroy)
        self.calc_button.pack(side='left')
        self.quit_button.pack(side='left')


        self.gallons_frame.pack()
        self.miles_frame.pack()
        self.mpg_frame.pack()
        self.button_frame.pack()

    def calc_mpg(self):
        self.gallons = float(self.gallons_entry.get())
        self.miles = float(self.miles_entry.get())

        self.miles_per_gallon = self.miles / self.gallons

        self.mpg.set(str(round(self.miles_per_gallon)))

car_mpg = MPG()