Python3: GUI later cannot display output properly? - python-3.x

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()

Answer 1

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.