code: def lookups(self, request, model_admin):
          
          list_of_countries = []
  
          # We don't need the country_count but we need to annotate them in order
          # to group the results.
          qs = Venue.objects.exclude(country='') \
                              .values('country') \
                              .annotate(country_count=Count('country')) \
                              .order_by('country')
          for obj in qs:
              country = obj['country']
              list_of_countries.append(
                  (country, Venue.COUNTRIES[country])
              )
  
          return sorted(list_of_countries, key=lambda c: c[1])
docs: Returns a list of tuples like:
  
              [
                  ('AU', 'Australia'),
                  ('GB', 'UK'),
                  ('US', 'USA'),
              ]
  
          One for each country that has at least one Venue.
          Sorted by the label names.