Python3: GUI later cannot display output properly?

Question

I'm designing a GUI application that converts between celsius and fahrenheit. For now, there're primarily two problems that I'm not able to tackle:

1) When I enter an integer that needs to be converted based on the given conversion formula, the Label from tkinter cannot display the output properly. In fact, it shows something like this:

<conversionModel.Conversion object at 0x1057b11d0>

which made it really difficult for debug to a beginner like me.

2) There's a quitButton, thought which we can destroy() the GUI application. The problem is that when I close the GUI by clicking the red cross of the window, the Shell says:

_tkinter.TclError: can't invoke "destroy" command: application has been destroyed

I checked answers to other questions regarding the same problem, it turned out that it was because this GUI application was destroyed before closing. I had no idea how to address this particular problem.

Below are three pieces of code written in Model/View/Controller form:

The Model in conversionModel.py:

class Conversion:

        """
        class Conversion is the Model for a celsius-fahrenheit conversion
        application. It converts celsius into fahrenheit and fahrenheit into
        celsius.
        """

        def toCelsius(self, temp):
            return (5 / 9) * (temp - 32)

        def toFahrenheit(self, temp):
            return ((9 / 5) * temp) + 32

The View in conversionView.py:

import tkinter

class MyFrame(tkinter.Frame):

def __init__(self, controller):
    tkinter.Frame.__init__(self)
    self.pack()
    self.controller = controller

    self.tempEntry = tkinter.Entry()
    self.tempEntry.insert(0, "0")
    self.tempEntry.pack({"side": "left"})        

    self.celsiusButton = tkinter.Button(self)
    self.celsiusButton["text"] = "Celsius"
    self.celsiusButton["command"] = self.controller.buttonToC
    self.celsiusButton.pack({"side": "left"})

    self.fahrenheitButton = tkinter.Button(self)
    self.fahrenheitButton["text"] = "Fahrenheit"
    self.fahrenheitButton["command"] = self.controller.buttonToF
    self.fahrenheitButton.pack({"side": "left"})

    self.labelForOutput = tkinter.Label(self)
    self.labelForOutput["text"] = 0
    self.labelForOutput.pack ({"side": "left"})

    self.quitButton = tkinter.Button(self)
    self.quitButton["text"] = "Quit"
    self.quitButton["command"] =  self.quit
    self.quitButton.pack({"side": "left"})

The Controller in controller.py:

import tkinter
import conversionView
import conversionModel

class Controller:

    def __init__(self):
        root = tkinter.Tk()
        self.model = conversionModel.Conversion()
        self.view = conversionView.MyFrame(self)
        self.value = float(self.view.tempEntry.get())
        self.view.mainloop()
        root.destroy()

    def buttonToC(self):
        self.model.toCelsius(self.value)
        self.view.labelForOutput["text"] = str(self.model) + " °C"

    def buttonToF(self):
        self.model.toFahrenheit(self.value)
        self.view.labelForOutput["text"] = str(self.model) + " °F"

if __name__ == "__main__":
    c = Controller()

Mark Tolonen · Accepted Answer · 2016-06-16 06:10:51Z

3

For #1, you need to read the tempEntry control each time you do a conversion, and capture the result of the conversion for printing. As it is now you only read the tempEntry control on __init__, and str(self.model) just prints out the name of the model object. This should work:

def buttonToC(self):
    fahr = float(self.view.tempEntry.get())
    temp = self.model.toCelsius(fahr)
    self.view.labelForOutput["text"] = str(temp) + " °C"

def buttonToF(self):
    celsius = float(self.view.tempEntry.get())
    temp = self.model.toFahrenheit(celsius)
    self.view.labelForOutput["text"] = str(temp) + " °F"

For #2, I'm not familiar enough with Tk yet to know why the Quit button works correctly but the red X destroys the windows before you get around to calling root.destroy, but this should work around it:

self.view.mainloop()
 try:
    root.destroy()
except tkinter.TclError:
    pass

The Quit button needs the destroy, but the X button doesn't and throws an exception. This code just ignores the exception in the X button case.

answered Jun 16, 2016 at 6:10

Mark Tolonen

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1 Comment

Mixone Over a year ago

or add root.protocol("WM_DELETE_WINDOW", app.on_delete) where app.on_delete is what he wants to do when closing no?

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