2.3 currently has the following behaviour:

>>> 'hello world'.encode('quopri')
'hello=20world'
>>> 'hello world'.encode('quopri').decode('quopri')
'hello world'
>>> u'hello world'.encode('quopri')
'=00h=00e=00l=00l=00o=00=20=00w=00o=00r=00l=00d'
>>> u'hello world'.encode('quopri').decode('quopri')
'\x00h\x00e\x00l\x00l\x00o\x00 \x00w\x00o\x00r\x00l\x00d'

I think the quoted printable encoding method should
either implicitly convert Unicode strings to US-ASCII,
or raise an exception.