Well, you can make both Python 2 & 3 string msg types be bytes with a note that bytes is the same as str in Python2.
$ python2
Python 2.7.13 (default, Jul 21 2017, 03:24:34)
>>> a = str('123')
>>> type(a)
<type 'str'>
>>> a = bytes('123')
>>> type(a)
<type 'str'>