temp_gui.py

#!/usr/bin/env python2
from Tkinter import *

# Input value 
input_value = 0
# Output value
output_value = 0
# Output Location
output_field = None

def CelsiusToFahrenheit():
	global output_field
	v = input_value.get()
	
	if not v:	return
	if v == 0.0:	return
	else:
		output_field.delete(0, END)
		output_field.insert(0, (v * 9.0/5.0) + 32)

def FahrenheitToCelsius():
	global output_field
	v = input_value.get()
	
	if not v:		return
	if v == 0.0:		return
	else:
		output_field.delete(0, END)
		output_field.insert(0, (v - 32) * (5.0/9.0))

def create_window():
	global input_value
	global output_value
	global output_field
	
	win = Tk()

	frame1 = Frame(win)
	frame1.pack()

	Label(frame1, text="Input").grid(row=0, column=0, sticky=W)
	input_value = DoubleVar()
	trash = Entry(frame1, textvariable=input_value)
	trash.grid(row=0, column=1, sticky=W)

	Label(frame1, text="Output").grid(row=1, column=0, sticky=W)
	output_value = DoubleVar()
	output_field = Entry(frame1, textvariable=output_value)
	output_field.grid(row=1, column=1, sticky=W)

	frame2 = Frame(win) # Row of buttons
	frame2.pack()
	b1 = Button(frame2,text="Fahrenheit To Celsius ", command=FahrenheitToCelsius)
	b2 = Button(frame2,text="Celsius To Fahrenheit", command=CelsiusToFahrenheit)
	b1.pack(side=LEFT)
	b2.pack(side=LEFT)

	return win

win = create_window()
win.mainloop()