code: def find_string(regex, s):
      
      m = re.search(regex, s)
      if m is None:
          return None
      return m.groups()[0]
docs: Find a string using a given regular expression. 
      If the string cannot be found, returns None.
      The regex should contain one matching group, 
      as only the result of the first group is returned.
  
      s - The string to search.
      regex - A string containing the regular expression.
      
      Returns a unicode string or None.