class DayMixin

def get_day(self):
    "Return the day for which this view should display data"
    day = self.day
    if day is None:
        try:
            day = self.kwargs['day']
        except KeyError:
            try:
                day = self.request.GET['day']
            except KeyError:
                raise Http404(_(u"No day specified"))
    return day

def get_day_format(self):
    """
    Get a day format string in strptime syntax to be used to parse the day
    from url variables.
    """
    return self.day_format

def get_next_day(self, date):
    """
    Get the next valid day.
    """
    next = date + datetime.timedelta(days=1)
    return _get_next_prev_month(self, next, is_previous=False, use_first_day=False)

def get_previous_day(self, date):
    """
    Get the previous valid day.
    """
    prev = date - datetime.timedelta(days=1)
    return _get_next_prev_month(self, prev, is_previous=True, use_first_day=False)