diff --git a/scrapy/trunk/scrapy/conf/core_settings.py b/scrapy/trunk/scrapy/conf/core_settings.py
index 74501c26c..70da5c802 100644
--- a/scrapy/trunk/scrapy/conf/core_settings.py
+++ b/scrapy/trunk/scrapy/conf/core_settings.py
@@ -11,6 +11,7 @@ USER_AGENT = '%s/%s' % (BOT_NAME, BOT_VERSION)
 DOWNLOAD_TIMEOUT = 180      # 3mins
 CONCURRENT_DOMAINS = 8    # number of domains to scrape in parallel
 REQUESTS_PER_DOMAIN = 8     # max simultaneous requests per domain
+CACHE2_EXPIRATION_SECS = 48 * 60 * 60 # seconds while cached response is still valid
 
 LOG_ENABLED = True  #
 LOGLEVEL = 'DEBUG'   # default loglevel
diff --git a/scrapy/trunk/scrapy/contrib/downloadermiddleware/cache.py b/scrapy/trunk/scrapy/contrib/downloadermiddleware/cache.py
index 773d3d99d..66f8a99ae 100644
--- a/scrapy/trunk/scrapy/contrib/downloadermiddleware/cache.py
+++ b/scrapy/trunk/scrapy/contrib/downloadermiddleware/cache.py
@@ -111,7 +111,12 @@ class Cache(object):
 
     def is_cached(self, domain, key):
         requestpath = self.requestpath(domain, key)
-        return os.path.exists(requestpath)
+        if os.path.exists(requestpath):
+            with open(os.path.join(requestpath, 'meta_data')) as f:
+                metadata = eval(f.read())
+            return datetime.datetime.now() <= metadata['timestamp'] + datetime.timedelta(seconds=settings.getint('CACHE2_EXPIRATION_SECS'))
+        else:
+            return False
 
     def retrieve_response(self, domain, key):
         """
diff --git a/scrapy/trunk/scrapy/http/request.py b/scrapy/trunk/scrapy/http/request.py
index 2c0623ed1..84d7377ad 100644
--- a/scrapy/trunk/scrapy/http/request.py
+++ b/scrapy/trunk/scrapy/http/request.py
@@ -1,6 +1,6 @@
 import urllib
 import warnings
-from sha import sha
+from hashlib import sha1
 from copy import copy
 from base64 import urlsafe_b64encode
 
@@ -149,7 +149,8 @@ class Request(object):
                     headers = dict([(k, v) for k, v in self.headers.items() if k.lower() not in keys])
 
         # fingerprint generation
-        fp = sha(canonicalize(self.url))
+        fp = sha1()
+        fp.update(canonicalize(self.url))
         fp.update(self.method)
 
         if self.body and self.method in ['POST', 'PUT']: