old_contents: from django.contrib import admin
  from django.utils.translation import ugettext_lazy as _
  
  class CountryFilter(admin.SimpleListFilter):
      """
      A country filter for Django admin that only returns a list of countries related to the model.
      """
      title = _('Country')
      parameter_name = 'country'
  
      def lookups(self, request, model_admin):
          return set([
              (obj.country, obj.country.name) for obj in model_admin.model.objects.exclude(
                  country__isnull=True
              ).exclude(country__exact='')
          ])
  
      def queryset(self, request, queryset):
          if self.value():
              return queryset.filter(country=self.value())
          else:
              return queryset
  
  
new_contents: from django.contrib import admin
  from django.utils.encoding import force_text
  from django.utils.translation import ugettext as _
  
  
  class CountryFilter(admin.FieldListFilter):
      """
      A country filter for Django admin that only returns a list of countries
      related to the model.
      """
      title = _('Country')
  
      def expected_parameters(self):
          return [self.field.name]
  
      def choices(self, changelist):
          yield {
              'selected': self.value() is None,
              'query_string': changelist.get_query_string(
                  {}, [self.field.name]),
              'display': _('All'),
          }
          for lookup, title in self.lookup_choices(changelist):
              yield {
                  'selected': self.value() == force_text(lookup),
                  'query_string': changelist.get_query_string(
                      {self.field.name: lookup}, []),
                  'display': title,
              }
  
      def lookup_choices(self, changelist):
          codes = changelist.queryset.values_list(self.field.name, flat=True)
          for k, v in self.field.get_choices(include_blank=False):
              if k in codes:
                  yield k, v
  
subject: Change the admin filter to a FieldListFilter