def _join_multiline_values(self):
        defaults = self.default_section, self._defaults
        all_sections = itertools.chain((defaults,),
                                       self._sections.items())
        for section, options in all_sections:
            for name, val in options.items():
                if isinstance(val, list):
                    val = '\n'.join(val).rstrip()
                options[name] = self._interpolation.before_read(self,
                                                                section,
                                                                name, val)