*: python3 update

Main changes are:

1. python3 is more strict when compare str and byte, it raise error. thus we need to encode and decode when do comparaison

2. unicode is removed in python3, to keep compability, i use six.string_types which (str, unicode) in Python 2, (str,) in Python 3

- if normalize and isinstance(item, (str, unicode)):
+ if normalize and isinstance(item, six.string_types + (bytes, )):