Well, I cannot imagine any situation when that would happen. `line_index >= 0` is an additional guard, just to be on the safe side. If `line_index` were negative, autopep8 would not blow up (even if the result -- indenting everything by one level -- would be wrong). But now I think it's better to end up with an OutOfBound exception -- users are more likely to report a bug if they see a traceback rather than an inappropriate result; so I've removed this assertion.