Calculate stack value's

[michalmonday]

It takes string as input and strings are easy to modify/organise. You can do this:

eval(str(s.pop()) + symbol + str(s.pop()))

and it automatically replaces this part that you posted:

if symbol == "+":
         plus = s.pop() + s.pop()
     elif symbol == "-":
         plus = s.pop() - s.pop()
     elif symbol == "*":
         plus = s.pop() * s.pop()
     elif symbol == "/":
         plus = s.pop() / s.pop()

You can also have a list of symbols and format them all into 1 eval function.