def _extract_error():
error_num = errno()<EOL>try:<EOL><INDENT>error_string = os.strerror(error_num)<EOL><DEDENT>except (ValueError):<EOL><INDENT>return str_cls(error_num)<EOL><DEDENT>if isinstance(error_string, str_cls):<EOL><INDENT>return error_string<EOL><DEDENT>return _try_decode(error_string)<EOL>
Extracts the last OS error message into a python unicode string

:return:
    A unicode string error message