def execute(self, fragment, pretty_format=True):
        """
        Run or aggregate a query fragment

        Concat the fragment to any stored fragments. If they form a complete
        query, run it and return the result. If not, store them and return
        None.

        """
        self.fragments = (self.fragments + "\n" + fragment).lstrip()
        try:
            line_parser.parseString(self.fragments)
        except ParseException:
            pass
        else:
            self.last_query = self.fragments.strip()
            self.fragments = ""
            return super(FragmentEngine, self).execute(self.last_query, pretty_format)
        return None
Run or aggregate a query fragment

        Concat the fragment to any stored fragments. If they form a complete
        query, run it and return the result. If not, store them and return
        None.