Exercise 6.2.7: Add, Subtract, or Multiply : codehs

user1 = int(input("Choose a number: "))
user2 = int(input("Choose another number: "))
op = input("Choose an operation to be preformed on these numbers (add, subtract, multiply): ")

def add():
    user3 = user1 + user2
    print str(user1) + " + " + str(user2) + " = " + str(user3)

def sub():
    user3 = user1 - user2
    print str(user1) + " - " + str(user2) + " = " + str(user3)

def times():
    user3 = user1 * user2
    print str(user1) + " * " + str(user2) + " = " + str(user3)


if op == "add":
    add()
elif op == "subtract":
    sub()
elif op == "multiply":
    times()
else:
    print "that is an invalid answer!"