rpn.py

#!/usr/bin/env python3

import operator

operators = {
        '+': operator.add,
        '-': operator.sub,
        '*': operator.mul,
        '/': operator.floordiv,
        '^': operator.pow,
}

def calculate(arg):
    stack = list()
    for token in arg.split():
        try:
            value = int(token)
            stack.append(value)
        except ValueError:
            function = operators[token]
            arg2 = stack.pop()
            arg1 = stack.pop()
            result = function(arg1, arg2) 
            stack.append(result)

        #print(stack)
    if len(stack) != 1:
        raise TypeError('malformed input')
    return stack.pop()

def main():
    while True:
        result = calculate(input("rpn calc> "))
        print(result)

if __name__ == '__main__': # Note: that's "underscore underscore n a m e ..."
    main()