[Over to python-dev. Jaco noticed that writing Unicode objects to a StringIO object stopped working in 2.2, see http://mail.python.org/pipermail/xml-sig/2001-December/006891.html ] Marc-Andre writes
Actually, I think that this is a bug in the documentation, not the code. StringIO and cStringIO were never meant to work on anything but strings and memory buffers.
IMO, "strings" should include both byte strings and Unicode strings. Mixing them may not be allowed, but that is a different story. In fact, there is an open bug (#216388) that cStringIO rejects Unicode objects. If that gets fixed, we get the funny scenario that StringIO rejects Unicode object, whereas cStringIO accepts them.
The note that Fred added to the docs about StringIO's capability of storing Unicode in it's buffer list is simply an artifact of the implementation.
There are many developers who take this note literally. Claiming that this was not intentional is a mistake.
Please use the .encode() method on Unicode objects before writing them to a StringIO object.
If you want to end up with a byte string, this is a good idea. But I think it is pointless to require encoding them when you want to end up with a Unicode string; you'd have to invoke unicode() on the result, for no apparent reason but a bug in the StringIO implementation. Regards, Martin