The unicode() docs say:

"If errors is 'strict' (the default), a ValueError is
raised on errors..."

This is not true; ValueError is only raised on
conversion errors.  There are other exceptions that can
be raised:

Python 2.1.2 (#1, Jan 18 2002, 18:05:45) 
[GCC 2.95.4  (Debian prerelease)] on linux2
Type "copyright", "credits" or "license" for more
information.

>>> unicode("abc", "nonexistent codec")
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
LookupError: unknown encoding

Looking at src/Objects/unicodeobject.c, there are lots
of other exceptions that can be raised.  The
documentation should probably be clarified.