Remove Roman numbers

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I have a text which contains latin numbers, like I, II etc which cometimes followed by dot (I.) and some other times without a dot (I). I want to remove them by using regular expressions in python. I can define the following function, but seems quite basic and takes lots of time. I was wondering if there any other way that I could remove them?

def clean(text):
  text = text.replace("Ι.", '&')
  text = text.replace("II.", '&')
  text = text.replace("III.", '&')
  text = text.replace("IV.", '&')
  text = text.replace("V.", '&')
  text = text.replace("VI.", '&')
  text = text.replace("VII.", '&')
  text = text.replace("VIII.", '&')
  text = text.replace("IX.", '&')
  text = text.replace("X.", '&')
  text = text.replace("XI.", '&')
  text = text.replace("XII.", '&')
  text = text.replace("XIII", '&')
  text = text.replace("XIV.", '&')

  return text
python regex
2 Answers

Use

def clean(text):
    pattern = r"\b(?=[MDCLXVIΙ])M{0,4}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})([IΙ]X|[IΙ]V|V?[IΙ]{0,3})\b\.?"
    return re.sub(pattern, '&', text)

See regex proof. Add more non-standard letters like Ι if necessary.

EXPLANATION

--------------------------------------------------------------------------------
  \b                       the boundary between a word char (\w) and
                           something that is not a word char
--------------------------------------------------------------------------------
  (?=                      look ahead to see if there is:
--------------------------------------------------------------------------------
    [MDCLXVIΙ]          any character of: 'M', 'D', 'C', 'L',
                             'X', 'V', 'I', '&', '#', '9', '2', '1',
                             ';'
--------------------------------------------------------------------------------
  )                        end of look-ahead
--------------------------------------------------------------------------------
  M{0,4}                   'M' (between 0 and 4 times (matching the
                           most amount possible))
--------------------------------------------------------------------------------
  (                        group and capture to \1:
--------------------------------------------------------------------------------
    CM                       'CM'
--------------------------------------------------------------------------------
   |                        OR
--------------------------------------------------------------------------------
    CD                       'CD'
--------------------------------------------------------------------------------
   |                        OR
--------------------------------------------------------------------------------
    D?                       'D' (optional (matching the most amount
                             possible))
--------------------------------------------------------------------------------
    C{0,3}                   'C' (between 0 and 3 times (matching the
                             most amount possible))
--------------------------------------------------------------------------------
  )                        end of \1
--------------------------------------------------------------------------------
  (                        group and capture to \2:
--------------------------------------------------------------------------------
    XC                       'XC'
--------------------------------------------------------------------------------
   |                        OR
--------------------------------------------------------------------------------
    XL                       'XL'
--------------------------------------------------------------------------------
   |                        OR
--------------------------------------------------------------------------------
    L?                       'L' (optional (matching the most amount
                             possible))
--------------------------------------------------------------------------------
    X{0,3}                   'X' (between 0 and 3 times (matching the
                             most amount possible))
--------------------------------------------------------------------------------
  )                        end of \2
--------------------------------------------------------------------------------
  (                        group and capture to \3:
--------------------------------------------------------------------------------
    [IΙ]                any character of: 'I', '&', '#', '9',
                             '2', '1', ';'
--------------------------------------------------------------------------------
    X                        'X'
--------------------------------------------------------------------------------
   |                        OR
--------------------------------------------------------------------------------
    [IΙ]                any character of: 'I', '&', '#', '9',
                             '2', '1', ';'
--------------------------------------------------------------------------------
    V                        'V'
--------------------------------------------------------------------------------
   |                        OR
--------------------------------------------------------------------------------
    V?                       'V' (optional (matching the most amount
                             possible))
--------------------------------------------------------------------------------
    [IΙ]{0,3}           any character of: 'I', '&', '#', '9',
                             '2', '1', ';' (between 0 and 3 times
                             (matching the most amount possible))
--------------------------------------------------------------------------------
  )                        end of \3
--------------------------------------------------------------------------------
  \b                       the boundary between a word char (\w) and
                           something that is not a word char
--------------------------------------------------------------------------------
  \.?                      '.' (optional (matching the most amount
                           possible))
user_113298900

Pleae, read first this How do you match only valid roman numerals with a regular expression?

If any regexp shown there is good enough, please use that. If not read on.

Hope this helps, but it is not complete. You have to write a test for valid roman numbers, because the regexp finds any combination of roman numerals. Related: Check if an input is a valid roman numeral

import re

MAYBE_ROMAN = re.compile(r'(\b[MDCLXVI]+\b)(\.)?', re.I)  # I = ignore case (optional)

def is_roman(num):
    # TODO!
    return True

def replace_roman(match):
    roman = match.group(1)
    if is_roman(roman):
        return '&' # replacement
    return roman # unchanged

test = "roman MCMLXXXVIII. roman XVII notroman MADXXXL invalid MILLI"
result = re.sub(MAYBE_ROMAN, replace_roman, test)
print(result)
user_53788160
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