python 2.7 and unicode (one more time)

[random832 at fastmail.us]

On Thu, Nov 20, 2014, at 07:35, Peter Otten wrote:
> >>> "%s nötig %s" % (u"üblich", u"ähnlich")
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 4: 
> ordinal not in range(128)

This is surprising to me - why is it trying to decode the format string,
rather than encode the arguments?