Gets or creates a log.

        :rtype: Timebucketedlog

def get_or_create(self, log_name, bucket_size):
        """
        Gets or creates a log.

        :rtype: Timebucketedlog
        """
        try:
            return self[log_name]
        except RepositoryKeyError:
            return start_new_timebucketedlog(log_name, bucket_size=bucket_size)