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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 days_at_time(days, t, tz, day_offset=0):
 """ Create an index of days at time ``t``, interpreted in timezone ``tz``. The returned index is localized to UTC. Parameters days : DatetimeIndex An index of dates (represented as midnight). t : datetime.time The time to apply as an offset to each day in ``days``. tz : pytz.timezone The timezone to use to interpret ``t``. day_offset : int The number of days we want to offset @days by Examples -------- In the example below, the times switch from 13:45 to 12:45 UTC because March 13th is the daylight savings transition for US/Eastern. All the times are still 8:45 when interpreted in US/Eastern. ['2016-03-12 13:45:00+00:00', '2016-03-13 12:45:00+00:00', '2016-03-14 12:45:00+00:00'] """

    days = pd.DatetimeIndex(days).tz_localize(None)
    if len(days) == 0:
        return days.tz_localize(UTC)

    # Offset days without tz to avoid timezone issues.
    delta = pd.Timedelta(
        days=day_offset,
        hours=t.hour,
        minutes=t.minute,
        seconds=t.second,
    )
    return (days + delta).tz_localize(tz).tz_convert(UTC)