> How about raising a TypeError if ``all(isinstance(l, str) for l in
> fromlist)`` is False? That would make the exception message less clearer
> since we can't include the "[...] not 'bytes'" part though.

    for l in fromlist:
        if not isinstance(l, str):
            raise TypeError(...)

Note also that you can get an arbitrary error if fromlist is not a sequence.

Actually this issue doesn't look very important for Python 3, since it is 
unlikely that non-string is passed in fromlist. Unlike to Python 2 where you 
can pass unicode if just use unicode_literals. Other solution for Python 2 is 
allowing unicode in fromlist. Perhaps this would increase compatibility with 
Python 3.