Adapt to python3 shelve.open behavior changes

When running tests between python2 and python3, shelve.open's behavior
has changed. These changes make it so that a previous run of one python
version of tests will not interfere with the current run. There are
still some issues with the database filename which may need to be
addressed.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/saml2/cache.py b/src/saml2/cache.py
index d14978e7..ae00afb8 100644
--- a/src/saml2/cache.py
+++ b/src/saml2/cache.py
@@ -23,7 +23,7 @@ class CacheError(SAMLError):
 class Cache(object):
     def __init__(self, filename=None):
         if filename:
-            self._db = shelve.open(filename, writeback=True)
+            self._db = shelve.open(filename, writeback=True, protocol=2)
             self._sync = True
         else:
             self._db = {}