old_contents: import datetime
  
  from django.db import models
  from django.contrib.auth.models import User
  from django.core.urlresolvers import reverse
  from django.utils.translation import ugettext_lazy as _
  
  
  class Announcement(models.Model):
      """
      A single announcement.
      """
      DISMISSAL_NO = 1
      DISMISSAL_SESSION = 2
      DISMISSAL_PERMANENT = 3
      
      DISMISSAL_CHOICES = [
          (DISMISSAL_NO, "No Dismissals Allowed"),
          (DISMISSAL_SESSION, "Session Only Dismissal"),
          (DISMISSAL_PERMANENT, "Permanent Dismissal Allowed")
      ]
      
      title = models.CharField(_("title"), max_length=50)
      content = models.TextField(_("content"))
      creator = models.ForeignKey(User, verbose_name=_("creator"))
      creation_date = models.DateTimeField(_("creation_date"), default=datetime.datetime.now)
      site_wide = models.BooleanField(_("site wide"), default=False)
      members_only = models.BooleanField(_("members only"), default=False)
      dismissal_type = models.IntegerField(choices=DISMISSAL_CHOICES, default=DISMISSAL_SESSION)
      publish_start = models.DateTimeField(_("publish_start"), default=datetime.datetime.now)
      publish_end = models.DateTimeField(_("publish_end"), blank=True, null=True)
      
      def get_absolute_url(self):
          return reverse("announcement_detail", args=[self.pk])
      
      def dismiss_url(self):
          if self.dismissal_type != Announcement.DISMISSAL_NO:
              return reverse("announcement_dismiss", args=[self.pk])
      
      def __unicode__(self):
          return self.title
      
      class Meta:
          verbose_name = _("announcement")
          verbose_name_plural = _("announcements")
  
  
  class Dismissal(models.Model):
      
      user = models.ForeignKey(User, related_name="announcement_dismissals")
      announcement = models.ForeignKey(Announcement, related_name="dismissals")
      dismissed_at = models.DateTimeField(default=datetime.datetime.now)
  
  
new_contents: from django.db import models
  from django.contrib.auth.models import User
  from django.core.urlresolvers import reverse
  from django.utils import timezone
  from django.utils.translation import ugettext_lazy as _
  
  
  class Announcement(models.Model):
      """
      A single announcement.
      """
      DISMISSAL_NO = 1
      DISMISSAL_SESSION = 2
      DISMISSAL_PERMANENT = 3
      
      DISMISSAL_CHOICES = [
          (DISMISSAL_NO, "No Dismissals Allowed"),
          (DISMISSAL_SESSION, "Session Only Dismissal"),
          (DISMISSAL_PERMANENT, "Permanent Dismissal Allowed")
      ]
      
      title = models.CharField(_("title"), max_length=50)
      content = models.TextField(_("content"))
      creator = models.ForeignKey(User, verbose_name=_("creator"))
      creation_date = models.DateTimeField(_("creation_date"), default=timezone.now)
      site_wide = models.BooleanField(_("site wide"), default=False)
      members_only = models.BooleanField(_("members only"), default=False)
      dismissal_type = models.IntegerField(choices=DISMISSAL_CHOICES, default=DISMISSAL_SESSION)
      publish_start = models.DateTimeField(_("publish_start"), default=timezone.now)
      publish_end = models.DateTimeField(_("publish_end"), blank=True, null=True)
      
      def get_absolute_url(self):
          return reverse("announcement_detail", args=[self.pk])
      
      def dismiss_url(self):
          if self.dismissal_type != Announcement.DISMISSAL_NO:
              return reverse("announcement_dismiss", args=[self.pk])
      
      def __unicode__(self):
          return self.title
      
      class Meta:
          verbose_name = _("announcement")
          verbose_name_plural = _("announcements")
  
  
  class Dismissal(models.Model):
      user = models.ForeignKey(User, related_name="announcement_dismissals")
      announcement = models.ForeignKey(Announcement, related_name="dismissals")
      dismissed_at = models.DateTimeField(default=timezone.now)
  
subject: Switch to using timezone.now instead of datetime.now