evaluate_postfix.py

class Stack():
    def __init__(self):
        self.items = []
    def push(self,item):
        self.items.append(item)
    def pop(self):
        return self.items.pop()
    def is_empty(self):
        return self.items==[]
    def peek(self):
        if not self.is_empty():
            return self.items[-1]
    def show_stack(self):
        return self.items

obj = Stack()
def evaluatePostfix(exp): 
    for i in exp: 
        # If the scanned character is an operand 
        # (number here) push it to the stack 
        if i.isdigit(): 
            obj.push(i) 
        # If the scanned character is an operator, 
        # pop two elements from stack and apply it. 
        else: 
            val1 = obj.pop() 
            val2 = obj.pop() 
            obj.push(str(eval(val2 + i + val1))) 

    return int(obj.pop()) 
 
exp = str(input("Enter the string\n"))
print ("postfix evaluation result: "+ str(evaluatePostfix(exp)))