meterer.get_period_strings()

        Return the period strings for the specified time (defaulting to the
        current time if not specified).

def get_period_strs(self, now=None):
        """
        meterer.get_period_strings()

        Return the period strings for the specified time (defaulting to the
        current time if not specified).
        """
        if now is None:
            now = self.dt.utcnow()

        year_str = "%04d" % now.year
        month_str = "%04d-%02d" % (now.year, now.month)
        day_str = "%04d-%02d-%02d" % (now.year, now.month, now.day)
        hour_str = "%04d-%02d-%02dT%02d" % (
            now.year, now.month, now.day, now.hour)

        # Note: The week number may be in the previous year during the last
        # days of the year.
        isocal = now.isocalendar()
        week_str = "%04d-W%02d" % (isocal[0], isocal[1])

        return {
            "year": year_str,
            "month": month_str,
            "day": day_str,
            "hour": hour_str,
            "week": week_str,
        }