A terrible way of creating a RPN calculator in Python 2

rpn.py

# -*- coding: utf-8 -*-

from sys import argv

class Stack:
     def __init__(self):
         self.items = []

     def isEmpty(self):
         return self.items == []

     def push(self, item):
         self.items.append(item)

     def pop(self):
         return self.items.pop()

     def peek(self):
         return self.items[len(self.items)-1]

     def size(self):
         return len(self.items)

def fOrI(s):
    def isfloat(x):
        try:
            a = float(x)
        except ValueError:
            return False
        else:
            return True
    
    def isint(x):
        try:
            a = float(x)
            b = int(a)
        except ValueError:
            return False
        else:
            return a == b
    
    if isint(s):
        return int(s)
    elif isfloat(s):
        return float(s)

def solveRpn(math):
    s = Stack()
    
    for i in math:
        if i == "+":
            a = s.pop()
            b = s.pop()
            
            s.push( a+b )
            
        elif i == "-":
            a = s.pop()
            b = s.pop()
            
            s.push( a-b )
            
        elif i == "*":
            a = s.pop()
            b = s.pop()
            
            s.push( a*b )
        
        elif i == "/":
            a = s.pop()
            b = s.pop()
            
            s.push( a/b )
        
        else:
            s.push( fOrI(i) )
            
    print( s.pop() )
        

solveRpn(argv)