Set comprehensions the way they are done in Python3.
        They're more other comprehensions, e.g. set comprehensions
        See if we can combine code.

def setcomprehension_walk3(self, node, collection_index):
        """Set comprehensions the way they are done in Python3.
        They're more other comprehensions, e.g. set comprehensions
        See if we can combine code.
        """
        p = self.prec
        self.prec = 27

        code = Code(node[1].attr, self.scanner, self.currentclass)
        ast = self.build_ast(code._tokens, code._customize)
        self.customize(code._customize)
        ast = ast[0][0][0]
        store = ast[3]
        collection = node[collection_index]

        n = ast[4]
        list_if = None
        assert n == 'comp_iter'

        # find innermost node
        while n == 'comp_iter':
            n = n[0] # recurse one step
            # FIXME: adjust for set comprehension
            if n == 'list_for':
                store = n[2]
                n = n[3]
            elif n in ('list_if', 'list_if_not', 'comp_if', 'comp_if_not'):
                # FIXME: just a guess
                if n[0].kind == 'expr':
                    list_if = n
                else:
                    list_if = n[1]
                n = n[2]
                pass
            pass

        assert n == 'comp_body', ast

        self.preorder(n[0])
        self.write(' for ')
        self.preorder(store)
        self.write(' in ')
        self.preorder(collection)
        if list_if:
            self.preorder(list_if)
        self.prec = p