Index: django/contrib/sessions/middleware.py
===================================================================
--- django/contrib/sessions/middleware.py	(revisión: 6364)
+++ django/contrib/sessions/middleware.py	(copia de trabajo)
@@ -4,13 +4,15 @@
 import datetime
 import time
 
+engine = __import__(settings.SESSION_ENGINE, {}, {}, [''])
+
 TEST_COOKIE_NAME = 'testcookie'
 TEST_COOKIE_VALUE = 'worked'
 
 class SessionMiddleware(object):
 
     def process_request(self, request):
-      engine = __import__(settings.SESSION_ENGINE, {}, {}, [''])
+      global engine
       request.session = engine.SessionStore(request.COOKIES.get(settings.SESSION_COOKIE_NAME, None))
 
     def process_response(self, request, response):
Index: django/contrib/sessions/backends/base.py
===================================================================
--- django/contrib/sessions/backends/base.py	(revisión: 6364)
+++ django/contrib/sessions/backends/base.py	(copia de trabajo)
@@ -104,13 +104,12 @@
     def _get_session(self):
         # Lazily loads session from storage.
         self.accessed = True
-        try:
+        if hasattr(self, '_session_cache'):
             return self._session_cache
-        except AttributeError:
-            if self.session_key is None:
-                self._session_cache = {}
-            else:
-                self._session_cache = self.load()
+        if self._session_key is None:
+            self._session_cache = {}
+        else:
+            self._session_cache = self.load()
         return self._session_cache
 
     _session = property(_get_session)