Note that with the -3 option Python 2.7 already warns about incompatibilities. 

>>> 'abc'.encode('base64')
__main__:1: DeprecationWarning: 'base64' is not a text encoding; use codecs.encode() to handle arbitrary codecs
'YWJj\n'
>>> 'YWJj\n'.decode('base64')
__main__:1: DeprecationWarning: 'base64' is not a text encoding; use codecs.decode() to handle arbitrary codecs
'abc'
>>> u'abc'.decode('ascii')
__main__:1: DeprecationWarning: decoding Unicode is not supported in 3.x
u'abc'