If you use Eventlet on Python 2.5 - bad news. Sample script to check: # relies on virtualenv activated or eventlet installed globally if python --version 2>&1 |fgrep -q 'Python 2.5' ; then if pip freeze |fgrep -q eventlet ; then echo 'bad news, read on' else echo ok fi else echo ok fi As discussed here https://github.com/eventlet/eventlet/issues/6 we're going to drop Python 2.5 support in some near future. Previous releases are still available for download in PyPi. I encourage everybody to repost this message to your friends and colleagues. If this change touches anybody, please, respond: - by email eventletdev@lists.secondlife.com - in Google+ https://plus.google.com/109869205442495270563/posts/GveGYMzubsp - in Github issue https://github.com/eventlet/eventlet/issues/6