Looking at the code, it seems that if it finds a unicode object on the first pass (the sizing pass), it punts and returns PyUnicode_Join(self, seq), which is the sequence from above and not necessarily the original object (orig), and starts over. In the worst-case scenario, you have a long sequence of strings with one unicode string at the end...
Actually, I guess I'm a little surprised that str.join(arg) doesn't require arg to be an iterator that returns str instances. unicode.join(arg) can afford to be a little more flexible. I wonder how common it is to pass a mixture of str and unicode to str.join(). -- http://mail.python.org/mailman/listinfo/python-list
