Python: pass an argument defined into a functionA to a functionB by pressing a button inside a functionC. No global variables

I have some problems when I want to pass an argument defined by a function1, to a function2 that I'm calling by pressing a button.

I'd like to print 'ABC' when I press the button, by passing 'ABC', defined in function1, to function2 when I press the button. I also need to keed the definition of 'ABC' in function1 and to print by using function2. I'd like to avoid global variables. Thank you

from tkinter import *
from tkinter import ttk        

def function1():
    var1=str('ABC')
    print(var1)
    return var1

def function2(var1):
    print('var1='+str(var1))

def function3():
    root = Tk()
    button = ttk.Button(root, text = "Click Me")
    button.pack()
    var1=str()
    button.config(command=lambda:function2(var1))
    root.mainloop()

function1()
function3()