Simple Django event calendar template tag

##### Here is the template tag code. It goes in a file named 
# "event_tags.py" in a subdirectory of your app called "templatetags".
#####

from calendar import HTMLCalendar
from django import template
from datetime import date
from itertools import groupby

from django.utils.html import conditional_escape as esc

register = template.Library()

def do_event_calendar(parser, token):
    """
    The template tag's syntax is {% event_calendar year month event_list %}
    """

    try:
        tag_name, year, month, event_list = token.split_contents()
    except ValueError:
        raise template.TemplateSyntaxError, "%r tag requires three arguments" % token.contents.split()[0]
    return EventCalendarNode(year, month, event_list)


class EventCalendarNode(template.Node):
    """
    Process a particular node in the template. Fail silently.
    """

    def __init__(self, year, month, event_list):
        try:
            self.year = template.Variable(year)
            self.month = template.Variable(month)
            self.event_list = template.Variable(event_list)
        except ValueError:
            raise template.TemplateSyntaxError

    def render(self, context):
        try:
            # Get the variables from the context so the method is thread-safe.
            my_event_list = self.event_list.resolve(context)
            my_year = self.year.resolve(context)
            my_month = self.month.resolve(context)
            cal = EventCalendar(my_event_list)
            return cal.formatmonth(int(my_year), int(my_month))
        except ValueError:
            return          
        except template.VariableDoesNotExist:
            return


class EventCalendar(HTMLCalendar):
    """
    Overload Python's calendar.HTMLCalendar to add the appropriate events to
    each day's table cell.
    """

    def __init__(self, events):
        super(EventCalendar, self).__init__()
        self.events = self.group_by_day(events)

    def formatday(self, day, weekday):
        if day != 0:
            cssclass = self.cssclasses[weekday]
            if date.today() == date(self.year, self.month, day):
                cssclass += ' today'
            if day in self.events:
                cssclass += ' filled'
                body = ['<ul>']
                for event in self.events[day]:
                    body.append('<li>')
                    body.append('<a href="%s">' % event.get_absolute_url())
                    body.append(esc(event.series.primary_name))
                    body.append('</a></li>')
                body.append('</ul>')
                return self.day_cell(cssclass, '<span class="dayNumber">%d</span> %s' % (day, ''.join(body)))
            return self.day_cell(cssclass, '<span class="dayNumberNoEvents">%d</span>' % (day))
        return self.day_cell('noday', '&nbsp;')

    def formatmonth(self, year, month):
        self.year, self.month = year, month
        return super(EventCalendar, self).formatmonth(year, month)

    def group_by_day(self, events):
        field = lambda event: event.date_and_time.day
        return dict(
            [(day, list(items)) for day, items in groupby(events, field)]
        )

    def day_cell(self, cssclass, body):
        return '<td class="%s">%s</td>' % (cssclass, body)

# Register the template tag so it is available to templates
register.tag("event_calendar", do_event_calendar)

##### Here's code for the view to look up the event objects for to put in 
# the context for the template. It goes in your app's views.py file (or 
# wherever you put your views).
#####

def named_month(month_number):
    """
    Return the name of the month, given the number.
    """
    return date(1900, month_number, 1).strftime("%B")

def this_month(request):
    """
    Show calendar of events this month.
    """
    today = datetime.now()
    return calendar(request, today.year, today.month)


def calendar(request, year, month, series_id=None):
    """
    Show calendar of events for a given month of a given year.
    ``series_id``
    The event series to show. None shows all event series.

    """

    my_year = int(year)
    my_month = int(month)
    my_calendar_from_month = datetime(my_year, my_month, 1)
    my_calendar_to_month = datetime(my_year, my_month, monthrange(my_year, my_month)[1])

    my_events = Event.objects.filter(date_and_time__gte=my_calendar_from_month).filter(date_and_time__lte=my_calendar_to_month)
    if series_id:
        my_events = my_events.filter(series=series_id)

    # Calculate values for the calendar controls. 1-indexed (Jan = 1)
    my_previous_year = my_year
    my_previous_month = my_month - 1
    if my_previous_month == 0:
        my_previous_year = my_year - 1
        my_previous_month = 12
    my_next_year = my_year
    my_next_month = my_month + 1
    if my_next_month == 13:
        my_next_year = my_year + 1
        my_next_month = 1
    my_year_after_this = my_year + 1
    my_year_before_this = my_year - 1
    return render_to_response("cal_template.html", { 'events_list': my_events,
                                                        'month': my_month,
                                                        'month_name': named_month(my_month),
                                                        'year': my_year,
                                                        'previous_month': my_previous_month,
                                                        'previous_month_name': named_month(my_previous_month),
                                                        'previous_year': my_previous_year,
                                                        'next_month': my_next_month,
                                                        'next_month_name': named_month(my_next_month),
                                                        'next_year': my_next_year,
                                                        'year_before_this': my_year_before_this,
                                                        'year_after_this': my_year_after_this,
    }, context_instance=RequestContext(request))

##### Here is the code to load and use the template tag in a template.

{% load event_tags %}

<div id="calendar">
    {% event_calendar year month event_list %}
</div>