static_url being cached?

[L-R]

I have different settings for DEV and PROD environments. My settings file looks like : 

if on_server :

   STATIC_DIR = some_S3_bucket_url

if on_dev:

  STATIC_DIR = static/

Then in my main file, I define my application normally : 

application = tornado.web.Application([

    (r"/", MyHandler),

],debug=settings.DEBUG, static_path=settings.STATIC_DIR)

Now, when I deploy on the server, Tornado still tries to serve from the static/ folder, which it shouldn't. In my handler, settings.STATIC_DIR returns the right URL (s3 url), and even if I change the static/ url in the dev settings to anything else, Tornado still tries to serve from static/. I tried clearing my cache, deleted .pyc files...what could be going on?

Thanks.