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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def save(self, config=None):
 """Saves config to config files. Args: config (configobj.ConfigObj):
 optional config object to save. Raises: dvc.config.ConfigError: thrown if failed to write config file. """

        if config is not None:
            clist = [config]
        else:
            clist = [
                self._system_config,
                self._global_config,
                self._repo_config,
                self._local_config,
            ]

        for conf in clist:
            if conf.filename is None:
                continue

            try:
                logger.debug("Writing '{}'.".format(conf.filename))
                dname = os.path.dirname(os.path.abspath(conf.filename))
                try:
                    os.makedirs(dname)
                except OSError as exc:
                    if exc.errno != errno.EEXIST:
                        raise
                conf.write()
            except Exception as exc:
                msg = "failed to write config '{}'".format(conf.filename)
                raise ConfigError(msg, exc)