old_contents: from django.contrib import admin
  from django.conf import settings
  from django.utils.translation import gettext_lazy as _
  
  from registry.models import Entry
  from registry.admin import EntryAdmin
  
  
  class CurrentConferenceFilter(admin.filters.SimpleListFilter):
      title = 'Current Conference'
      parameter_name = 'current'
  
      def lookups(self, request, model_admin):
          return [
              (None, _('Current')),
              ('other', _('Other')),
              ('all', _('All')),
          ]
  
      def queryset(self, request, queryset):
          if self.value() == 'all':
              return queryset
          elif self.value() == 'other':
              return queryset.exclude(key__startswith=f'{settings.CONFERENCE_DEFAULT_SLUG}')
  
          return queryset.filter(key__startswith=f'{settings.CONFERENCE_DEFAULT_SLUG}')
  
      def choices(self, changelist):
          for lookup, title in self.lookup_choices:
              yield {
                  'selected': self.value() == lookup,
                  'query_string': changelist.get_query_string({self.parameter_name: lookup}),
                  'display': title,
              }
  
  
  class PyConEntryAdmin(EntryAdmin):
      list_filter = (CurrentConferenceFilter, ) + EntryAdmin.list_filter
  
  
  admin.site.unregister(Entry)
  admin.site.register(Entry, PyConEntryAdmin)
  
new_contents: from django.contrib import admin
  from django.conf import settings
  from django.utils.translation import gettext_lazy as _
  
  from registry.models import Entry
  from registry.admin import EntryAdmin
  
  
  class CurrentConferenceFilter(admin.filters.SimpleListFilter):
      title = 'Current Conference'
      parameter_name = 'current'
  
      def lookups(self, request, model_admin):
          return [
              (None, _('Current')),
              ('other', _('Other')),
              ('all', _('All')),
          ]
  
      def queryset(self, request, queryset):
          if self.value() == 'all':
              return queryset
          elif self.value() == 'other':
              return queryset.exclude(key__startswith=settings.CONFERENCE_DEFAULT_SLUG)
  
          return queryset.filter(key__startswith=settings.CONFERENCE_DEFAULT_SLUG)
  
      def choices(self, changelist):
          for lookup, title in self.lookup_choices:
              yield {
                  'selected': self.value() == lookup,
                  'query_string': changelist.get_query_string({self.parameter_name: lookup}),
                  'display': title,
              }
  
  
  class PyConEntryAdmin(EntryAdmin):
      list_filter = (CurrentConferenceFilter, ) + EntryAdmin.list_filter
  
  
  admin.site.unregister(Entry)
  admin.site.register(Entry, PyConEntryAdmin)
  
subject: Remove unnecessary format strings