'''
20210923
R. Dawes

New features added in this version:
  In the previous version we used "float()" to convert the input
  from string to float.  But if the input string is something like "12a?78..5" then
  trying to convert it to a float will cause an execution error.
  
  We can catch the error and recover from it using the "try" and "except" controls.
  In use, they look like this:
  
       try:
            <something that might cause an error>
       except <the type of error that might have happened>:
            <what to do if the error occurred>
            
  In our situation, we are possibly going to be applying "float()" to a string that
  cannot be translated to a number.  This causes an error (technically called an
  exception) called ValueError, so this is what we look for.
  
  See the use of this in the "button_1_clicked" function below

'''

import tkinter as tk
import sys

window = tk.Tk()
window.title("Compare two numbers")
window.geometry("1200x800")


label_1 = tk.Label(window,text="Enter x in this box")
#add an entry box to accept input
entry_1 = tk.Entry(window, width = 10)

label_2 = tk.Label(window,text="Enter y in this box")
#add an entry box to accept input
entry_2 = tk.Entry(window, width = 10)


#add a text box to show output
text_1 = tk.Text(window,height = 10, width = 30)

#add a button - a clickable object

#add a function to react to button_1

def button_1_clicked():
   try:
      x = float(entry_1.get())
   except ValueError:
      x = None                          # if the input cannot be interpreted as a number
                                               # we assign x the value of None.  Later we will check
                                               # x to see if it equals None.  If so, we know the input
                                               # was invalid.
   try:
      y = float(entry_2.get())
   except ValueError:
      y = None     
      
   text_1.delete(1.0, tk.END)
   if (x == None) or (y == None):               # here we check to see if the input was
                                                                      # invalid.  If it was invalid, we put a
                                                                      # message in the Text box
      text_1.insert(tk.END, "Invalid Input")
   else:
      # now we know the input was successfully converted to floating point numbers
      if (x < y):
         text_1.insert(tk.END, str(x) + " < " + str(y))
      elif (x > y):
         text_1.insert(tk.END, str(x) + " > " + str(y))
      else:
         text_1.insert(tk.END, str(x) + " = " + str(y))


button_1 = tk.Button(window, text = "Compare Them", command = button_1_clicked)

#add a button to end execution

button_2 = tk.Button(window,text = "Exit", command = sys.exit)


label_1.grid(row = 0, column = 0)
entry_1.grid(row = 0, column = 1)
label_2.grid(row = 1, column = 0)
entry_2.grid(row = 1, column = 1)
button_1.grid(row = 2, column = 0)
text_1.grid(row = 2, column = 2)
button_2.grid(row = 75, column = 869)      # getting a bit carried away with the row and column

window.mainloop()