regex_pattern = r"^(M){0,3}(CM)?(D)?(CD)?(C){0,3}(XC)?(L)?(XL)?(X){0,3}(IX)?(V)?(IV)?(I){0,3}$"

Here, only M, C, X and I can repeat at most 3 times, others can occur 0 or 1 times

At first I came up with this:

regex_pattern = r"^(?!$)(M{1,3})?(CD|CM|D?C{1,3})?(XL|XC|L?X{1,3})?(IV|IX|V?I{1,3})?$"

But I see it can be done like this as well:

regex_pattern = r"^(?!$)M{0,3}(CD|CM|D?C{0,3})(XL|XC|L?X{0,3})(IV|IX|V?I{0,3})$"

Or even this way

regex_pattern = r"^(?!$)M{,3}(C[DM]|D?C{,3})(X[LC]|L?X{,3})(I[VX]|V?I{,3})$"

Not everyone in every country is familiar with Roman Numerals though..

The post about Validating Roman Numerals is intriguing! I love exploring various numeral systems and their validation techniques. By the way, if you're interested in cybersecurity and want to learn more about click here, they offer excellent resources to enhance your skills. Keep up the fascinating discussions!

Dumbest test so far.

regex_pattern = r"^(M{0,3})(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$"