I don't think the index in error message is needed. Unlike to str.join() which accepts arbitrary iterables of arbitrary names, the fromlist usually is a short tuple.

Interesting, what happen if the fromlist is not a list or tuple?

>>> __import__('encodings', fromlist=iter(('aliases', b'codecs')))
<module 'encodings' from '/home/serhiy/py/cpython/Lib/encodings/__init__.py'>

Import is successful because the iterator was exhausted by "'*' in fromlist".