docs: def clear_cache(modeladmin, request, queryset=None):
      """
      Clears media cache files such as thumbnails.
      """
      
      execute = request.POST.get('execute')
      
      files_in_storage = []
      storage = get_media_storage()
      cache_files_choices = []
      for storage_name in get_cache_files():
          link = mark_safe('<a href="%s">%s</a>' % (
              storage.url(storage_name), storage_name))
          cache_files_choices.append((storage_name, link))
  
      if not len(cache_files_choices):
          messages.warning(request, message=_('There are no cache files.'))
          return HttpResponseRedirect('')
  
      if execute:
          form = DeleteCacheFilesForm(queryset, cache_files_choices, request.POST)
          if form.is_valid():
              form.save()
              node = FileNode.get_top_node()
              message = ungettext('Deleted %i cache file.', 'Deleted %i cache files.', len(form.success_files)) % len(form.success_files)
              if len(form.success_files) == len(cache_files_choices):
                  message = '%s %s' % (_('The cache was cleared.'), message)
              messages.success(request, message=message)
              if form.error_files:
                  messages.error(request, message=_('The following files could not be deleted:')+' '+repr(form.error_files))
              return HttpResponseRedirect(node.get_admin_url())
  
      if not execute:
          if len(cache_files_choices) > 0:
              form = DeleteCacheFilesForm(queryset, cache_files_choices)
          else:
              form = None
  
      c = get_actions_context(modeladmin)
      c.update({
          'title': _('Clear cache'),
          'submit_label': _('Delete selected files'),
          'form': form,
          'select_all': 'selected_files',
      })
      return render_to_response('admin/media_tree/filenode/actions_form.html', c, context_instance=RequestContext(request))
  
      return HttpResponseRedirect('')