def _prepare_paths(self):
        """Set the value of {{base}} in paths if the base path is set in the
        configuration.

        :raises: ValueError

        """
        if config.BASE in self.paths:
            for path in [path for path in self.paths if path != config.BASE]:
                if config.BASE_VARIABLE in self.paths[path]:
                    self.paths[path] = \
                        self.paths[path].replace(config.BASE_VARIABLE,
                                                 self.paths[config.BASE])
        LOGGER.debug('Prepared paths: %r', self.paths)