code: def _ibis_sqlite_regex_extract(string, pattern, index):
      
      result = re.search(pattern, string)
      if result is not None and 0 <= index <= (result.lastindex or -1):
          return result.group(index)
      return None
docs: Extract match of regular expression `pattern` from `string` at `index`.
  
      Parameters
      ----------
      string : str
      pattern : str
      index : int
  
      Returns
      -------
      result : str or None