This is another case where leaving the str() is probably preferred.  Keep in mind that in Py2 six.text_type() is actually unicode() so switching it is actually changing the behavior of the code, and it should probably be left alone instead.  Just blindly switching all str()'s to six.text_type()'s most certainly not the correct action in many cases.

For those cases where the old code is already using unicode() or doing something else that could result in a unicode value then it should be examined more closely to see if using six.text_type() is more appropriate and is needed for Py2/Py3 compatibility.