Comment utiliser en boucle dans une instruction IF sur Python?

def change():
    if choice == 1:    #<--- issue here
        while True:
            amt = float(input("Enter amount of cash: $"))
            if amt >= a:
                print("Your change will be: ${:.2f}".format(amt - a))
                break
            else:
                print("Not enough, missing: ${:.2f}".format(a - amt))
                input("press enter to continue")


a = 15.60
b = 56.12
c = 89.53
d = 32.93
print("1. a: $15.60\t\t\t2. b: $56.12\n3. c: $89.53\t\t\t4. d: $32.93")
choice = input("Choose product (1-4): ")
change()
If I remove line 2, it would function properly but choice 1 would not be selected. I'd like it so this would run while choice 1 is selected. For some reason it's not allowing me to put an if statement before while loop. Is there a solution?