constant updates

[Mensa180]

Hello! I've been messing with tkinter and now have tried to make a MPG calculator using sliders.

My problem is that no matter how I move the sliders it does not update the mpg, I'm not sure what to tell the label to do for it to update.

I know the calculations themselves work because I made it print to the console as a test and it updated there.

import tkinter as tk


root = tk.Tk()
root.title('MPG calculator')

root.geometry("620x200+300+300")


scale = tk.Scale(root, label="Select a distance traveled.",
    from_=1, to=1500, tickinterval=0, resolution=1, length=600,
    showvalue='yes', orient='horizontal')

scale.set(500)

scale2 = tk.Scale(root, label="Select how large your fuel tank is.",
    from_=1, to=80, tickinterval=0, resolution=1, length=600,
    showvalue='yes', orient='horizontal')

scale.set(12)

dist = scale.get()
tank = scale2.get()
f = dist / tank
result = 'You get %s miles per gallon.' % (f)

label = tk.Label(root, text= result, bg='green')


scale.grid(row=2, columnspan=2)
scale2.grid(row=1, columnspan=2)
label.grid(row=4, columnspan=4, pady=5)

root.mainloop()

Thanks!

edit:
The attached file shows my problem. It shows 12 mpg no matter what.

[snippsat]

You need event handling.
Put this function at top after import like this.

import tkinter as tk

def on_move(value=0):
    f = scale.get()    
    label['text'] = f

Now you see that your down slider is working.
So now just figure out the calulate stuff,and you have a nice program.

[snippsat]

Forget i made change to this 2 lines to.

scale = tk.Scale(root, label="Select a distance traveled.",
    from_=1, to=1500, tickinterval=0, resolution=1, length=600,
    showvalue='yes', orient='horizontal',command=on_move)

label = tk.Label(root, text='---', bg='green')

[Mensa180]

Thanks it's all sorted out now, a nifty little program :).