code: def guid_check_convert(guid, allow_none=False):
          
          if isinstance(guid, string_types):
              return ensure_unicode(UUID(guid).hex)
          elif guid is None and allow_none:
              return None
          else:
              raise ValueError('guid must be a string')
docs: Take a GUID in the form of hex string "32" or "8-4-4-4-12".
          Returns hex string "32" or raises ValueError: badly formed hexadecimal UUID string