In my excitement about the big changes in PyMongo 2.4, I forgot to mention a smaller one you should watch out for: from now on, if the initial connection to MongoDB fails, PyMongo raises ConnectionFailure instead of AutoReconnect. This is a more intuitive exception to throw, but it does mean you need to change your exception handlers. If you've been doing this:

    connection = Connection('mongo_host')
except AutoReconnect:
    print "Can't connect to MongoDB!"

...then you need to start catching ConnectionFailure from now on. This change only applies to the initial creation of Connection or ReplicaSetConnection, not to the AutoReconnect exceptions PyMongo raises if there's a network error on an established connection. The change does apply to PyMongo 2.4's new MongoClient and MongoReplicaSetClient classes.

Since AutoReconnect inherits from ConnectionFailure, you might already be catching ConnectionFailure. In that case, carry on.

Here's the full bug report that motivated the change. This is subtle enough that I missed it a few times in PyMongo's own unittests, so check your code and make sure you're catching the right exception.