[Python-3000] email libraries: use byte or unicode strings?

[Stephen J. Turnbull]

Andrew McNamara writes:

 > However - charset encoding is part of the MIME spec, so users have a
 > reasonable expectation that the mime lib will present them with unicode.
 > So the API needs to be unicode.

It needs to /include/ unicode functionality.  However, this might very
well be lazy (a function which automatically resends a message may not
need to decode the MIME parts, for example).

So I think there should be three layers: one corresponding more or less
to raw SMTP---all bytes; one which handles mail as text---all unicode;
and one which handles the transitions---which needs phasers set to
"kill" any data in incorrect format.

I also suggest that these three levels of functionality are
intertwingled enough (at the RFC level) that it does not make sense to
separate them into more than one module.