In Python, all functionality related to regular expressions is contained in the re module.
|$||end of the string|
|^||start of the string|
|\b||a word boundary must occur right here|
|M?||Matches an optionally M character|
'\' character in a string must itself be escaped. To work around that you can use a raw string, by prefixing the string with the letter r.
Example: match 'ROAD' when it's a whole word by itself anywhere in the string.
re.sub(r'\bROAD\b', 'RD.', s)