days
previous_start = fromdate.replace(tzinfo=None) -
timedelta(days=daysback + 1)
previous_start = format_date(to_datetime(previous_start, req.tz),
- format='%Y-%m-%d', tzinfo=req.tz)
+ format='iso8601', tzinfo=req.tz)
add_link(req, 'prev', req.href.timeline(from_=previous_start,
authors=authors,