import Tkinter

# global variables
temp_c = None
temp_f = None

def convert():

    global temp_c
    global temp_f

    try:
        val = temp_c.get()
        temp_f.set((val * 9.0 / 5) + 32)
    except:
        pass

# main window
window = Tkinter.Tk()
window.title("Temperature Converter")

# main container
frame = Tkinter.Frame(window)

# lay out the main container, specify that we want it to grow with window size
frame.pack(fill=Tkinter.BOTH, expand=True)

# allow middle cell of grid to grow when window is resized
frame.columnconfigure(1, weight=1)
frame.rowconfigure(1, weight=1)

# variables for holding temperature data
temp_c = Tkinter.DoubleVar()
temp_f = Tkinter.DoubleVar()

# create widgets
entry_celsius = Tkinter.Entry(frame, width=7, textvariable=temp_c)
label_unitc = Tkinter.Label(frame, text="degrees C")
label_equal = Tkinter.Label(frame, text="is equal to")
label_fahrenheit = Tkinter.Label(frame, textvariable=temp_f)
label_unitf = Tkinter.Label(frame, text="degrees F")
button_convert = Tkinter.Button(frame, text="Convert", command=convert)

# lay out widgets
entry_celsius.grid(row=0, column=1, padx=5, pady=5)
label_unitc.grid(row=0, column=2, padx=5, pady=5, sticky=Tkinter.W)
label_equal.grid(row=1, column=0, padx=5, pady=5, sticky=Tkinter.E)
label_fahrenheit.grid(row=1, column=1, padx=5, pady=5)
label_unitf.grid(row=1, column=2, padx=5, pady=5, sticky=Tkinter.W)
button_convert.grid(row=2, column=1, columnspan=2, padx=5, pady=5, sticky=Tkinter.E)

# Place cursor in entry box by default
entry_celsius.focus()

# Run forever!
window.mainloop()