old_contents: from django.contrib import admin
  from reversion import VersionAdmin
  
  from base.admin import PrettyFilterMixin, RestrictedCompetitionAdminMixin
  from base.util import admin_commentable, editonly_fieldsets
  
  from .models import Post
  
  
  # Reversion-enabled Admin for problems
  @admin_commentable
  @editonly_fieldsets
  class PostAdmin(RestrictedCompetitionAdminMixin,
                  VersionAdmin):
  
      list_display = (
          'title',
          'published',
          'get_sites',
          'added_by',
          'added_at',
      )
  
      list_filter = (
          'published',
          'added_at',
          'added_by'
      )
  
      search_fields = (
          'text',
          'title'
      )
  
      readonly_fields = (
          'added_by',
          'modified_by',
          'added_at',
          'modified_at'
      )
  
      prepopulated_fields = {"slug": ("title",)}
  
      fieldsets = (
          (None, {
              'fields': ('title', 'slug', 'text', 'sites', 'published', 'gallery')
          }),
      )
  
      editonly_fieldsets = (
          ('Details', {
              'classes': ('grp-collapse', 'grp-closed'),
              'fields': ('added_by', 'modified_by', 'added_at', 'modified_at')
          }),
      )
  
      class Media:
          js = [
              'grappelli/tinymce/jscripts/tiny_mce/tiny_mce.js',
              'grappelli/tinymce_setup/tinymce_setup.js',
          ]
  
  # Register to the admin site
  admin.site.register(Post, PostAdmin)
  
new_contents: from django.contrib import admin
  from reversion import VersionAdmin
  
  from base.admin import PrettyFilterMixin, RestrictedCompetitionAdminMixin
  from base.util import admin_commentable, editonly_fieldsets
  
  from .models import Post
  
  
  # Reversion-enabled Admin for problems
  @admin_commentable
  @editonly_fieldsets
  class PostAdmin(RestrictedCompetitionAdminMixin,
                  VersionAdmin):
  
      list_display = (
          'title',
          'published',
          'get_sites',
          'added_by',
          'added_at',
      )
  
      list_filter = (
          'published',
          'sites',
          'added_at',
          'added_by'
      )
  
      search_fields = (
          'text',
          'title'
      )
  
      readonly_fields = (
          'added_by',
          'modified_by',
          'added_at',
          'modified_at'
      )
  
      prepopulated_fields = {"slug": ("title",)}
  
      fieldsets = (
          (None, {
              'fields': ('title', 'slug', 'text', 'sites', 'published', 'gallery')
          }),
      )
  
      editonly_fieldsets = (
          ('Details', {
              'classes': ('grp-collapse', 'grp-closed'),
              'fields': ('added_by', 'modified_by', 'added_at', 'modified_at')
          }),
      )
  
      class Media:
          js = [
              'grappelli/tinymce/jscripts/tiny_mce/tiny_mce.js',
              'grappelli/tinymce_setup/tinymce_setup.js',
          ]
  
  # Register to the admin site
  admin.site.register(Post, PostAdmin)
  
subject: Add ability to filter posts by site