def create_summary(self):
        """Return a summary.

        See also the notes on ignore_self in the class as well as the
        initializer documentation.

        """
        if not self.ignore_self:
            res = summary.summarize(muppy.get_objects())
        else:
            # If the user requested the data required to store summaries to be
            # ignored in the summaries, we need to identify all objects which
            # are related to each summary stored.
            # Thus we build a list of all objects used for summary storage as
            # well as a dictionary which tells us how often an object is
            # referenced by the summaries.
            # During this identification process, more objects are referenced,
            # namely int objects identifying referenced objects as well as the
            # correspondind count.
            # For all these objects it will be checked wether they are
            # referenced from outside the monitor's scope. If not, they will be
            # subtracted from the snapshot summary, otherwise they are
            # included (as this indicates that they are relevant to the
            # application).

            all_of_them = []  # every single object
            ref_counter = {}  # how often it is referenced; (id(o), o) pairs
            def store_info(o):
                all_of_them.append(o)
                if id(o) in ref_counter:
                    ref_counter[id(o)] += 1
                else:
                    ref_counter[id(o)] = 1

            # store infos on every single object related to the summaries
            store_info(self.summaries)
            for k, v in self.summaries.items():
                store_info(k)
                summary._traverse(v, store_info)

            # do the summary
            res = summary.summarize(muppy.get_objects())

            # remove ids stored in the ref_counter
            for _id in ref_counter:
                # referenced in frame, ref_counter, ref_counter.keys()
                if len(gc.get_referrers(_id)) == (3):
                    summary._subtract(res, _id)
            for o in all_of_them:
                # referenced in frame, summary, all_of_them
                if len(gc.get_referrers(o)) == (ref_counter[id(o)] + 2):
                    summary._subtract(res, o)

        return res
    def test_traverse(self):
        """Test that all objects of a summary are traversed."""
        touched = []
        def remember(o, touched):
            touched.append(o)

        s = [['row1', 1, 2], ['row2', 3, 4], ['row3', 5, 6]]
        summary._traverse(s, remember, touched)

        self.assert_(s in touched)
        for row in s:
            self.assert_(row in touched)
            for item in row:
                self.assert_(item in touched)