old_contents: from django.db import models
  from django.contrib.sites.models import Site
  from django.utils.translation import ugettext as _
  
  
  class Feedback(models.Model):
      site = models.ForeignKey(Site, verbose_name=_('site'))
      url = models.CharField(max_length=255, verbose_name=_('url'))
      subject = models.CharField(max_length=255, blank=True, null=True,
              verbose_name=_('subject'))
      email = models.EmailField(blank=True, null=True, verbose_name=_('email'))
      text = models.TextField(verbose_name=_('text'))
  
      def __unicode__(self):
          return u'%s: %s' % (self.url, self.subject)
  
new_contents: from django.db import models
  from django.contrib.sites.models import Site
  from django.utils.translation import ugettext as _
  
  
  class Feedback(models.Model):
      site = models.ForeignKey(Site, verbose_name=_('site'))
      url = models.CharField(max_length=255, verbose_name=_('url'))
      subject = models.CharField(max_length=255, blank=True, null=True,
              verbose_name=_('subject'))
      email = models.EmailField(blank=True, null=True, verbose_name=_('email'))
      text = models.TextField(verbose_name=_('text'))
  
      def __unicode__(self):
          return u'{url}: {subject}'.format(url=self.url, subject=self.subject)
  
subject: use new string formatting