<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def formatday(self, day, weekday):
 """ Return a day as a table cell with a link if entries are published this day. """

        if day and day in self.day_entries:
            day_date = date(self.current_year, self.current_month, day)
            archive_day_url = reverse('zinnia:entry_archive_day',
                                      args=[day_date.strftime('%Y'),
                                            day_date.strftime('%m'),
                                            day_date.strftime('%d')])
            return '<td class="%s entry"><a href="%s" '\
                   'class="archives">%d</a></td>' % (
                       self.cssclasses[weekday], archive_day_url, day)

        return super(Calendar, self).formatday(day, weekday)