encoding: add converter between native str and byte string This kind of encoding conversion is unavoidable on Python 3.

encoding: factor out unicode variants of from/tolocal() Unfortunately, these functions will be commonly used on Python 3.

py3: use next() to obtain next item from inner generator of generatorset .next attribute does not exist on Python 3. As this function seems to really care about the overhead of the Python interpreter, I follow the way of micro optimization.

py3: rewrite itervalues() as values() by importer I'm not a great fan of these importer magics, but this should be okay since "itervalues" seems as unique name as "iteritems".