old_contents: import django
  from django.conf import settings
  from django.contrib.sessions.models import SessionManager
  from django.db import models
  from django.utils.translation import ugettext_lazy as _
  
  
  class Session(models.Model):
      """
      Session objects containing user session information.
  
      Django provides full support for anonymous sessions. The session
      framework lets you store and retrieve arbitrary data on a
      per-site-visitor basis. It stores data on the server side and
      abstracts the sending and receiving of cookies. Cookies contain a
      session ID -- not the data itself.
  
      Additionally this session object providers the following properties:
      ``user``, ``user_agent`` and ``ip``.
      """
      session_key = models.CharField(_('session key'), max_length=40,
                                     primary_key=True)
      session_data = models.TextField(_('session data'))
      expire_date = models.DateTimeField(_('expiry date'), db_index=True)
      objects = SessionManager()
  
      class Meta:
          verbose_name = _('session')
          verbose_name_plural = _('sessions')
  
      def get_decoded(self):
          return SessionStore(None, None).decode(self.session_data)
  
      user = models.ForeignKey(getattr(settings, 'AUTH_USER_MODEL', 'auth.User'),
                               null=True)
      user_agent = models.CharField(max_length=200)
      last_activity = models.DateTimeField(auto_now=True)
      if django.VERSION[:2] >= (1, 6):
          ip = models.GenericIPAddressField(verbose_name='IP')
      else:
          ip = models.IPAddressField(verbose_name='IP')
  
  
  # At bottom to avoid circular import
  from .backends.db import SessionStore
  
new_contents: import importlib
  
  import django
  from django.conf import settings
  from django.contrib.sessions.models import SessionManager
  from django.db import models
  from django.utils.translation import ugettext_lazy as _
  
  
  class Session(models.Model):
      """
      Session objects containing user session information.
  
      Django provides full support for anonymous sessions. The session
      framework lets you store and retrieve arbitrary data on a
      per-site-visitor basis. It stores data on the server side and
      abstracts the sending and receiving of cookies. Cookies contain a
      session ID -- not the data itself.
  
      Additionally this session object providers the following properties:
      ``user``, ``user_agent`` and ``ip``.
      """
      session_key = models.CharField(_('session key'), max_length=40,
                                     primary_key=True)
      session_data = models.TextField(_('session data'))
      expire_date = models.DateTimeField(_('expiry date'), db_index=True)
      objects = SessionManager()
  
      class Meta:
          verbose_name = _('session')
          verbose_name_plural = _('sessions')
  
      def get_decoded(self):
          return SessionStore(None, None).decode(self.session_data)
  
      user = models.ForeignKey(getattr(settings, 'AUTH_USER_MODEL', 'auth.User'),
                               null=True)
      user_agent = models.CharField(max_length=200)
      last_activity = models.DateTimeField(auto_now=True)
      if django.VERSION[:2] >= (1, 6):
          ip = models.GenericIPAddressField(verbose_name='IP')
      else:
          ip = models.IPAddressField(verbose_name='IP')
  
  
  # At bottom to avoid circular import
  SessionStore = getattr(importlib.import_module(settings.SESSION_ENGINE), 'SessionStore')
  
subject: fix the bug: wrong SessionStore used, should be imported dynamically