Thanks for the report and patch.  This is not as easy as it sounds: The doc ambiguously uses “string”; the code clearly wants only byte strings (str); in the 3.x version, only character strings (unicode) are accepted; “raw” would suggest to me than only bytes make sense.

I would tend to edit the documentation but no the behavior, given that 2.7 is stable and this behavior has been present and documented for a long time.  Senthil, what’s your opinion?