Convert the Test Average GUI by adding a fourth test and a letter grade

import tkinter

class TestAvg:

def __init__(self):

# Create the main window.

self.main_window = tkinter.Tk()

# Create the five frames.

self.test1_frame = tkinter.Frame(self.main_window)

self.test2_frame = tkinter.Frame(self.main_window)

self.test3_frame = tkinter.Frame(self.main_window)

self.avg_frame = tkinter.Frame(self.main_window)

self.button_frame = tkinter.Frame(self.main_window)

# Create and pack the widgets for test 1.

self.test1_label = tkinter.Label(self.test1_frame,

text='Enter the score for test 1:')

self.test1_entry = tkinter.Entry(self.test1_frame,

width=10)

self.test1_label.pack(side='left')

self.test1_entry.pack(side='left')

# Create and pack the widgets for test 2.

self.test2_label = tkinter.Label(self.test2_frame,

text='Enter the score for test 2:')

self.test2_entry = tkinter.Entry(self.test2_frame,

width=10)

self.test2_label.pack(side='left')

self.test2_entry.pack(side='left')

# Create and pack the widgets for test 3.

self.test3_label = tkinter.Label(self.test3_frame,

text='Enter the score for test 3:')

self.test3_entry = tkinter.Entry(self.test3_frame,

width=10)

self.test3_label.pack(side='left')

self.test3_entry.pack(side='left')

# Create and pack the widgets for the average.

self.result_label = tkinter.Label(self.avg_frame,

text='Average:')

self.avg = tkinter.StringVar() # To update avg_label

self.avg_label = tkinter.Label(self.avg_frame,

textvariable=self.avg)

self.result_label.pack(side='left')

self.avg_label.pack(side='left')

# Create and pack the button widgets.

self.calc_button = tkinter.Button(self.button_frame,

text='Average',

command=self.calc_avg)

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')

# Pack the frames.

self.test1_frame.pack()

self.test2_frame.pack()

self.test3_frame.pack()

self.avg_frame.pack()

self.button_frame.pack()

# Start the main loop.

tkinter.mainloop()

# The calc_avg method is the callback function for

# the calc_button widget.

def calc_avg(self):

# Get the three test scores and store them

# in variables.

self.test1 = float(self.test1_entry.get())

self.test2 = float(self.test2_entry.get())

self.test3 = float(self.test3_entry.get())

# Calculate the average.

self.average = (self.test1 + self.test2 +

self.test3) / 3.0

# Update the avg_label widget by storing

# the value of self.average in the StringVar

# object referenced by avg.

self.avg.set(self.average)

# Create an instance of the TestAvg class.

test_avg = TestAvg()