gistfile1.txt

def main():
    PF1 = "124*+3-22+-3/2/3*"
    PF2 = "65-4*54/7*+9-9-"
    global tos
    tos = -1

    def push(s, elem):
        global tos
        tos = 1+tos
        s[tos] = elem

    def pop(s):
        global tos
        val = s[tos]
        tos = tos - 1
        return val

    def Calculator(expression):
        stack = [0] * len(expression)
        #use array of size expression

        def add(a, b):
            return (float(a) + float(b))

        def sub(a, b):
            return (float(b) - float(a))

        def mult(a, b):
            return (float(a) * float(b))

        def divide(a, b):
            return (float(b) / float(a))

        for x in expression:
            #if mult pop twice off stack
            push(stack, x)
            if x == '*':
                pop(stack)
                push(stack, mult(pop(stack), pop(stack)))
            elif x == '/':
                pop(stack)
                push(stack, divide(pop(stack), pop(stack)))
            elif x == '+':
                pop(stack)
                push(stack, add(pop(stack), pop(stack)))
            elif x == '-':
                pop(stack)
                push(stack, sub(pop(stack), pop(stack)))

        print(pop(stack))


    Calculator(PF1)
    Calculator(PF2)
    Calculator("64-1-2-3-4-")


if __name__ == "__main__":
    main()