text: from django.contrib.admin import SimpleListFilter
  from django.utils.translation import ugettext_lazy as _
  
  __all__ = [
      'ExpiredFilter',
      'RevokedFilter',
  ]
  
  
  class BooleanListFilter(SimpleListFilter):
  
      def lookups(self, request, model_admin):
          return (
              ('yes', _('Yes')),
              ('no', _('No')),
          )
  
  
  class ExpiredFilter(BooleanListFilter):
      title = _('Expired')
      parameter_name = 'expired'
  
      def queryset(self, request, queryset):
          if self.value() == 'yes':
              return queryset.expired().filter(expired=True)
  
          if self.value() == 'no':
              return queryset.expired().filter(expired=False)
  
  
  class RevokedFilter(BooleanListFilter):
      title = _('Revoked')
      parameter_name = 'revoked'
  
      def queryset(self, request, queryset):
          if self.value() == 'yes':
              return queryset.filter(revoked__isnull=False)
  
          if self.value() == 'no':
              return queryset.filter(revoked__isnull=True)
  