Reverse Polish Notation Python Version

rpn.py

# Reverse Polish notation demo
# Basic calulator for RPN expression only + / * - is supported.
# Allows ints and floats.

import math
stack = []

def IsNuber(s):
    is_num = True
    for n in s:
        if str.isdigit(n) or n == ".":
            is_num = True
        else:
            is_num = False
            break
    return is_num

def rpn(expression):
    parts = expression.split(" ")

    for s in parts:
        value = s.strip()
        if len(value):
            if IsNuber(value):
                stack.append(value)
            else:
                if value == "+":
                    # Pop of the values from the stack
                    a = stack.pop()
                    b = stack.pop()
                    res = float(a) + float(b)
                    stack.append(res)
                if value == "-":
                    # Pop of the values from the stack
                    a = stack.pop()
                    b = stack.pop()
                    res = float(b) - float(a)
                    stack.append(res)
                if value == "*":
                    # Pop of the values from the stack
                    a = stack.pop()
                    b = stack.pop()
                    res = float(a) * float(b)
                    stack.append(res)
                if value == "/":
                    # Pop of the values from the stack
                    a = stack.pop()
                    b = stack.pop()
                    res = float(b) / float(a)
                    stack.append(res)
    return float(stack.pop())

# Infix == (4 * (12 + 3) / 2 * (5 + 5) - (100 * 2))
expr = "4 12 3 + * 2 / 5 5 + * 100 2 * - 2 /"
print(rpn(expr))
# float test pi
expr = "22 7 /"
print(rpn(expr))