Python Tkinter StringVar issues

Question

I am trying to make a simple calculator for a game I play as a random project. I found myself very confused on how to go about doing this; I want the user to enter a number in the textbox and it will multiply that number by 64000 and display it in a label above. But, I cannot find out anywhere how to do this. This is just a small practice thing and im amazed I cannot figure it out. Please help meh! Here is my code:

from Tkinter import *

####The GUI#####
root = Tk()

#Title#
root.wm_title("TMF Coin Calculator")

####The Widgets####
a = StringVar()
b = StringVar()

def multiply_a():
    d = (int(a) * 64000)
    e = str(d)
    b.set(e)

b.trace("w", multiply_a)

#Top Label#

top_label = Label(root,  fg="red", text="Type the ammount of Coin Stacks you have.")
top_label.grid(row=0, column=0)

#The Output Label#
output_label = Label(root, textvariable=b, width = 20)
output_label.grid(row = 1, column=0)

#User Entry Box#
user_input_box = Entry(root, textvariable=a, width=30)
user_input_box.grid(row=2, column=0)

root.mainloop()

Answer 1

You need to trace the variable that changes: a . Then you need to define multiply_a() to handle an arbitrary number of arguments with *args (happens to be 3 arguments in this case, but *args is fine here).

Go from:

def multiply_a():
    d = (int(a) * 64000)
    e = str(d)
    b.set(e)

b.trace("w", multiply_a)

to:

def multiply_a(*args):
    try:
        myvar = int(a.get())
    except ValueError:
        myvar = 0
    b.set(myvar * 64000)

a.trace("w", multiply_a)

This will additionally use 0 if the entered value can't be turned into an int .