Using six would be fine. Initially I didn't want to add a new dependency to six, because there was only few places that needed updates. I can update pull request tomorrow with a version that uses six.

I don't mind adding a dependency on six. An update would be nice. Thanks for your work!

I updated with new version that uses six. I did not change dictionary iteration with .items() to use six, because it is mostly used to iterate over dictionary. In two places where dictionary is modified during iteration, I added explicit conversion to list.