What’s new in the next version of Tornado

In progress

Backwards-compatibility notes


  • tornado.concurrent.Future is now always thread-unsafe (previously it would be thread-safe if the concurrent.futures package was available). This improves performance and provides more consistent semantics. The parts of Tornado that accept Futures will accept both Tornado’s thread-unsafe Futures and the thread-safe concurrent.futures.Future.
  • tornado.concurrent.Future now includes all the functionality of the old TracebackFuture class. TracebackFuture is now simply an alias for Future.


  • The internals of the tornado.gen module have been rewritten to improve performance when using Futures, at the expense of some performance degradation for the older YieldPoint interfaces.
  • Performance of coroutines has been improved.
  • Coroutines no longer generate StackContexts by default, but they will be created on demand when needed.


  • IOLoop.add_handler and related methods now accept file-like objects in addition to raw file descriptors. Passing the objects is recommended (when possible) to avoid a garbage-collection-related problem in unit tests.


  • The callback argument to most IOStream methods is now optional. When called without a callback the method will return a Future for use with coroutines.


  • It is now possible to disable the default logging configuration by setting options.logging to None instead of the string “none”.


  • Now works on Python 2.6.


  • The stack context system now has less performance overhead when no stack contexts are active.


  • AsyncTestCase now attempts to detect test methods that are generators but were not run with @gen_test or any similar decorator (this would previously result in the test silently being skipped).
  • Better stack traces are now displayed when a test times out.


  • When gzip support is enabled, all text/* mime types will be compressed, not just those on a whitelist.


  • WebSocketHandler.close and WebSocketClientConnection.close now support code and reason arguments to send a status code and message to the other side of the connection when closing. Both classes also have close_code and close_reason attributes to receive these values when the other side closes.
  • The C speedup module now builds correctly with MSVC, and can support messages larger than 2GB on 64-bit systems.