Python - Transform a roman to an integer

Question

I've tried the following Python 3 code that transform from Roman to Integer.

The code is working fine at a glance. But there are certain problem happened when I input an integer number or string (ex: 1, 2 or any integer number, string) it shows some code error. I want when I input any thing except roman number (within 1 to 3999) it should return "Try again".

Here is my code:

class Solution(object):
   def romanToInt(self, s):
      """
      :type s: str
      :rtype: int
      """
      roman = {'I':1,'V':5,'X':10,'L':50,'C':100,'D':500,'M':1000,'IV':4,'IX':9,'XL':40,'XC':90,'CD':400,'CM':900}
      i = 0
      num = 0
      while i < len(s):
         if i+1<len(s) and s[i:i+2] in roman:
            num+=roman[s[i:i+2]]
            i+=2
         else:
            #print(i)
            num+=roman[s[i]]
            i+=1
      return num
ob1 = Solution()

message = str(input("Please enter your roman number: "))
if (ob1.romanToInt(message)) <= 3999:
   print (ob1.romanToInt(message))
else:
    print ("Try again")

Answer 1

Try this:

message = str(input("Please enter your roman number: "))
try:
    n = ob1.romanToInt(message)
    if n > 3999: raise Exception()
    print(n)
except Exception:
    print("Try again")