code: def parse_upstring(line):
      
      UP_STRING_REGEX = r"\[(U|_)+]"
  
      match = re.search(UP_STRING_REGEX, line)
      if match:
          return match.group().strip('[]')
      else:
          return None
docs: Parse the subsequent lines of a device array stanza in ``/proc/mdstat``
      for the "up" indictor string.
  
      Lines are expected to be like:
  
          129596288 blocks [2/2] [UU]
  
      or
  
          1318680576 blocks level 5, 1024k chunk, algorithm 2 [10/10] [UUU_UUUUUU]
  
      In particular, this method searchs for the string like ``[UU]`` which
      indicates whether component devices or up, ``U`` or down, ``_``.
  
      Parameters
      ----------
  
      line : str
          A single line from a device array stanza.
  
      Returns
      -------
  
          The string containing a series of ``U`` and ``\_`` characters if
          found in the string, and ``None`` if the uptime string is not found.