I'm confused as to how this unit test is passing:

    def test__eq__(self):
        s1 = set_type()
        s2 = other_type()
        if set_type != other_type:
            raises(TypeError, s1.__eq__, s2)
            return

When the code for PersistentSet looks like this:

    def __eq__(self, other):
        if not isinstance(other, PersistentSet):
            return False
        return self.data == other.data

Is it possible that raises() in Sancho is not working properly?  If so,
would you want to consider switching to regular unit tests?  That's what
we have done with our fork of Durus.  Converting the tests was easy, and
we run them using Nose.

P.S.  There are other tests that are similarly broken.

--
Patrick K. O'Brien
Orbtech       http://www.orbtech.com
Schevo        http://www.schevo.org
Louie         http://www.pylouie.org