Tkinter variable "Num1" referenced before assignment

Question

I’m very new to Tkinter and don’t know exactly what I’m doing. I have these two entry widgets which are both numbers when entered. Whenever I press the "run" button to multiply the numbers I get a "variable referenced before assignment error" and I’m not sure why.
Here’s the code:

    from tkinter import *

    root = Tk()

    def myClick1():
        Num1 = int(Num1.get())
        Num2 = int(Num2.get())
        print(Num1 * Num2)
    Num1 = Entry(root, bg = "black", fg = "red", border = 10, justify = RIGHT)
    Num2 = Entry(root, bg = "black", fg = "blue", border = 10, justify = RIGHT)

    RAD2=Radiobutton(root, text = "Run", command = myClick1, fg = "red", bg = "black", border = 12)

    RAD2.pack()
    Num1.pack()
    Num2.pack()
    root.mainloop()

Any help would be appreciated.

Asked By: Thornton Raza

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Source

Answer 1

In python, global variables such as Num1 and Num2 are available globally, as the name implies. However, if you try to assign a new value to a variable in a function, that variable automatically becomes local.

Thus, when you do Num1 = int(Num1.get()), Num1 is considered to be a local variable. And since you have not assigned a local variable named Num1 prior to this statement, Num1.get() fails.

If you rename the local variable Num1 and Num2 to something else, this will work.

def myClick1():
    num1 = int(Num1.get())
    num2 = int(Num2.get())
    print(num1 * num2)

Answered By: Bryan Oakley

Tkinter variable "Num1" referenced before assignment

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