Partitioning comments by date
I think this would a great situation to use itertools.groupby in.

datekey = lambda x: x.date
comments.sort(key=datekey)
date_comments = [list(group) for date, group in itertools.groupby(comments, datekey)]


This of course groups all your comments, not only the ones in your date range. I'd use filter to skip the ones out of your range if you can't make use of the extra days comments.