ImportError.__init__ sets only specified attributes ("msg", "name" or "path"), and left not explicitly specified attributes unchanged.

>>> err = ImportError('test', name='name')
>>> err.args, err.msg, err.name, err.path
(('test',), 'test', 'name', None)
>>> err.__init__(path='path')
>>> err.args, err.msg, err.name, err.path
((), 'test', 'name', 'path')

In above example err.__init__(path='path') sets attributes "args" and "path", but not "msg" and "name".

I'm not sure whether can this be considered as a bug.