One of the rather subtle issues with writing Python 2/3 code is that indexing on bytes in Python 2 returns a length-1 bytes object while in Python 3 it returns an int. Because ==/!= always returns True/False it can be a very subtle failure and tough to track down.
What do people think of extending -b/-bb in Python 3 to warn when performing equality between an int and a bytes object of any length? I don't want to restrict to length-1 bytes objects because people may be doing comparisons where the result can be length-1 or any other length and thus would still have a subtle bug to pick up. Do people think this would raise a ton of false-positives? Would people find it useful?