How do you match only valid roman numerals with a regular expression?

Question

Thinking about my other problem, i decided I can\'t even create a regular expression that will match roman numerals (let alone a context-free grammar that will generate them

Answer 1

The following expression worked for me to validate the roman number.

^M{0,4}(C[MD]|D?C{0,3})(X[CL]|L?X{0,3})(I[XV]|V?I{0,3})$

Here,

• M{0,4} will match thousands
• C[MD]|D?C{0,3} will match Hundreds
• X[CL]|L?X{0,3} will match Tens
• I[XV]|V?I{0,3} will match Units

Below is a visualization that helps to understand what it is doing, preceded by two online demos:

Debuggex Demo

Regex 101 Demo

Python Code:

import re
regex = re.compile("^M{0,4}(C[MD]|D?C{0,3})(X[CL]|L?X{0,3})(I[XV]|V?I{0,3})$")
matchArray = regex.match("MMMCMXCIX")