From 4ab240d53af95938c6a7e61f9d62aede34dcfc3d 2011-11-23 21:07:40
From: Thomas Kluyver <takowl@gmail.com>
Date: 2011-11-23 21:07:40
Subject: [PATCH] Specify protocol 2 for pickleshare, so objects stored by Python 3 can be used in Python 2.

---

diff --git a/IPython/utils/pickleshare.py b/IPython/utils/pickleshare.py
index fe14a44..e68d1fe 100755
--- a/IPython/utils/pickleshare.py
+++ b/IPython/utils/pickleshare.py
@@ -80,7 +80,9 @@ class PickleShareDB(collections.MutableMapping):
         parent = fil.parent
         if parent and not parent.isdir():
             parent.makedirs()
-        pickled = pickle.dump(value,fil.open('wb'))
+        # We specify protocol 2, so that we can mostly go between Python 2
+        # and Python 3. We can upgrade to protocol 3 when Python 2 is obsolete.
+        pickled = pickle.dump(value,fil.open('wb'), protocol=2)
         try:
             self.cache[fil] = (value,fil.mtime)
         except OSError,e: