def tag_filter(request, tag):
    now = datetime.datetime.now()
    concerts = Concert.objects.filter(tags__name__in=[tag])
                              .filter(date__gte=now).order_by('date')
    return render(request, 'concerts/calendar.html', {'concerts': concerts})

{% elif request.resolver_match.url_name == "tag_filter" %}
  <h1>Upcoming Events with "{{ concerts.0.tags.name }}" Tag</h1>
  {% endif %}