validating a text entry on tkinter

Question

I'm creating a program that allows the user to select a category and enter a value to calculate a charge. I would like to validate the text entry using my own validation file. However, when I run the program and enter nothing in the text entry, the error window keeps popping up over and over again. In addition, when I run the program and enter a valid number in the entry field, the charge comes out to 0.0, even though I have defined the calculation for the total charge.

Here is the program:

import tkinter
import tkinter.messagebox
import ValidationFile

validationObject = ValidationFile.ValidationClass ()

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

        self.top_frame = tkinter.Frame (self.main_window)
        self.middle_frame = tkinter.Frame (self.main_window)
        self.bottom_frame = tkinter.Frame (self.main_window)

        self.phone_var = tkinter.IntVar ()

        self.phone_var.set (1)

        self.pb1 = tkinter.Radiobutton (self.top_frame, \
                    text = 'Daytime (6:00 AM - 5:59 PM)', variable = self.phone_var, \
                    value = 0.12)
        self.pb2 = tkinter.Radiobutton (self.top_frame, \
                    text = 'Evening (6:00 PM - 11:59 PM)', variable = self.phone_var, \
                    value = 0.07)
        self.pb3 = tkinter.Radiobutton (self.top_frame, \
                    text = 'Off-Peak (Midnight - 5:50 AM)', variable = self.phone_var, \
                    value = 0.05)

        #pack phone buttons
        self.pb1.pack ()
        self.pb2.pack ()
        self.pb3.pack ()

        #create input and output buttons
        self.txtInput = tkinter.Entry (self.middle_frame, \
                                       width = 10)
        self.value = tkinter.StringVar ()

        self.lblOutput = tkinter.Label (self.middle_frame, \
                                        width = 10, textvariable = self.value)

        self.txtInput.pack()
        self.lblOutput.pack ()

        #create OK buton and QUIT button
        self.ok_button = tkinter.Button (self.bottom_frame, \
                        text = 'OK', command = self.show_choice)
        self.quit_button = tkinter.Button (self.bottom_frame, \
                        text = 'QUIT', command = self.main_window.destroy)

        #pack the buttons
        self.ok_button.pack (side = 'left')
        self.quit_button.pack (side = 'left')

        #pack the frames
        self.top_frame.pack ()
        self.middle_frame.pack ()
        self.bottom_frame.pack ()

        #start the mainloop
        tkinter.mainloop ()


    def show_choice (self):
        choice = self.phone_var.get ()
        value = -1
        while value == -1:
            valueEntry = self.txtInput.get()
            if valueEntry == '':
                value = -1
                tkinter.messagebox.showinfo (title = 'ERROR', \
                                             message = 'Please enter a valid number.')
            else:
                value = validationObject.checkFloat (valueEntry)

        total = choice * value
        self.value.set (total)

#create instance of MyGUI class
my_GUI = MyGUI ()

Here is the validation file:

#create validation class
class ValidationClass:

    def checkFloat (self, inputString):

        try:
            result = float (inputString)
        except Exception:
            return -1

        if result < 0:
            return -1
        else:
            return result

    def checkInteger (self, inputString):

        try:
            result = int (inputString)
        except Exception:
            return -1

        if result < 0:
            return -1
        else:
            return result

Answer 1

You made an infinite loop with while value == -1: . Nowhere in that loop do you pause to allow the user to try again. You don't need the loop at all:

def show_choice (self):
    valueEntry = self.txtInput.get()
    value = validationObject.checkFloat(valueEntry)
    if value == -1:
        tkinter.messagebox.showinfo (title = 'ERROR', \
                                         message = 'Please enter a valid number.')
    else:
        choice = self.phone_var.get()
        total = choice * value
        self.value.set (total)

Once you fix that you will have another problem: you use float values in your options but the variable is an IntVar, which can only handle integers. So "choice" will always be 0. You need to use DoubleVar instead.