When backported issue30876 to 3.5 I found that the lines

        elif not package:
            raise ImportError('attempted relative import with no known parent '
                              'package')

don't exist in 3.5. They where added in issue26367, but only in the 3.6 branch. The original example in issue26367 still returns a module with a wrong name in 3.5.

Why issue26367 changes were applied to 3.5 only partially? I afraid that the absence of this check may interfere with removing SystemError.