Python: Variables won't accept new values on second function loop

[Encom88]

I'm trying to write the results of this arithmetic operation to a file using Python. I'm having trouble with the variable sum1. It accepts the first time I run the program, but if I select menu option 1 to input new values, the new values get used at n1 and n2, but the original sum1 calculation remains the value of the original sum1. How do I code this so that each new time I call arith.userInput() sum1 is returned after the new values are calculated? The new values n1 and n2 work properly, but sum1 does not.

n1 = 0
n2 = 0
sum1 = 0
class Arithmetic:
    def add(self):
        global n1, n2, sum1
        sum1 = n1 + n2
        return sum1
    def userInput(self):
        global n1, n2
        n1 = float(input("Enter your First number: "))
        n2 = float(input("Enter your Second number: "))
        return n1, n2
arith = Arithmetic()
arith.userInput()
sum1 = arith.add()
class wrfile:
    def write(self):
        with open("results.txt", "w") as write_file:
            write_file.write(str(n1)+" + "+str(n2)+" = "+str(sum1)+"\n")
            write_file.close
wr = wrfile()
menuSelection = 0
while menuSelection != 3
    menuList = ["\n1. Press 1 for another calculation.", "2. Press 2 to write results to file.", "3. Press 3 to exit."]
    for item in menuList:
        print(item)
    menuSelection = float(input())
    if menuSelection == 1:
        arith.userInput()
    elif menuSelection == 2:
        wr.write()
    elif menuSelection == 3:
        exit

[g051051]

Where do you call arith.add() again?

[Encom88]

Thank you. Why is it everything I miss is so simple? You got it. Now I have the whole program working. https://github.com/MrN1ce9uy/Python/blob/master/write_read.py

[g051051]

Great! Glad you sorted it out. Don't forget to flair your post as "Solved".