code: def is_valid_uuid (uuid):
      
      try:
          if len (uuid) == 4:
              if int (uuid, 16) < 0: return False
          elif len (uuid) == 8:
              if int (uuid, 16) < 0: return False
          elif len (uuid) == 36:
              pieces = uuid.split ("-")
              if len (pieces) != 5 or \
                      len (pieces[0]) != 8 or \
                      len (pieces[1]) != 4 or \
                      len (pieces[2]) != 4 or \
                      len (pieces[3]) != 4 or \
                      len (pieces[4]) != 12:
                  return False
              [ int (p, 16) for p in pieces ]
          else:
              return False
      except ValueError: 
          return False
      except TypeError:
          return False
      return True
docs: is_valid_uuid (uuid) -> bool
  
      returns True if uuid is a valid 128-bit UUID.
  
      valid UUIDs are always strings taking one of the following forms:
          XXXX
          XXXXXXXX
          XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX
      where each X is a hexadecimal digit (case insensitive)