Oops... the dict part should have been "dict(lhs=first, rhs=second)":

    def failUnlessEqual(self, first, second, msg=None):
        """Fail if the two objects are unequal as determined by the '=='
           operator. Argument msg could optionally include string format
           operators named "lhs" and "rhs" (e.g., "%(lhs)r")
        """
        if not first == second:
            raise self.failureException, \
                  (msg or "%(lhs)r != %(rhs)r") % dict(lhs=first, rhs=second)