def _metric_history_keys(self, slugs, since=None, to=None,
                             granularity='daily'):
        if type(slugs) != list:
            slugs = [slugs]
        keys = []
        for slug in slugs:
            for date in self.r._date_range(granularity, since, to):
                keys += self.r._build_keys(slug, date, granularity)
        keys = list(dedupe(keys))
        return keys
generates the same list of keys used in ``get_metric_history``.
dataset/ETHPy150Open bradmontgomery/django-redis-metrics/redis_metrics/tests/test_models.py/TestR._metric_history_keys