def start_of_day(dtime_at=None):
dtime_at = datetime_or_now(dtime_at)<EOL>return datetime.datetime(dtime_at.year, dtime_at.month,<EOL>dtime_at.day, tzinfo=tzlocal())<EOL>
Returns the local (user timezone) start of day, that's,
time 00:00:00 for a given datetime