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

Im answering this question Regular Expression in Python for Roman Numerals here
because it was marked as an exact duplicate of this question.

It might be similar in name, but this is a specific regex question / problem
as can be seen by this answer to that question.

The items being sought can be combined into a single alternation and then
encased inside a capture group that will be put into a list with the findall()
function.
It is done like this :

>>> import re
>>> target = (
... r"this should pass v" + "\n"
... r"this is a test iii" + "\n"
... )
>>>
>>> re.findall( r"(?m)\s(i{1,3}v*|v)$", target )
['v', 'iii']

The regex modifications to factor and capture just the numerals are this :

 (?m)
 \s 
 (                     # (1 start)
      i{1,3} 
      v* 
   |  v
 )                     # (1 end)
 $