In order to get a -3 PyErr_WarnPy3k warning for unicode being passed to hashlib objects (a nice idea) I suggest creating an additonal 's*' like thing ('s3' perhaps?) in Python/getargs.c for that purpose rather than modifying all of the hashlib modules to accept an O, type check it and warn, and then re-parse it as a s* (that'd be a lot of tedious code duplication).