What’s new in the next version of Tornado

In progress

Highlights

• The new async/await keywords in Python 3.5 are supported. In most cases, async def can be used in place of the @gen.coroutine decorator. Inside a function defined with async def, use await instead of yield to wait on an asynchronous operation. Coroutines defined with async/await will be faster than those defined with @gen.coroutine and yield, but do not support some features including Callback/Wait or the ability to yield a Twisted Deferred.

tornado.auth

• New method OAuth2Mixin.oauth2_request can be used to make authenticated requests with an access token.

tornado.autoreload

• Fixed an issue with the autoreload command-line wrapper in which imports would be incorrectly interpreted as relative.

tornado.gen

• WaitIterator now supports the async for statement on Python 3.5.

tornado.httputil

• HTTPHeaders can now be pickled and unpickled.

tornado.ioloop

• IOLoop(make_current=True) now works as intended instead of raising an exception.
• The Twisted and asyncio IOLoop implementations now clear current() when they exit, like the standard IOLoops.

tornado.iostream

• Coroutine-style usage of IOStream now converts most errors into StreamClosedError, which has the effect of reducing log noise from exceptions that are outside the application’s control (especially SSL errors).
• StreamClosedError now has a real_error attribute which indicates why the stream was closed. It is the same as the error attribute of IOStream but may be more easily accessible than the IOStream itself.

tornado.locale

• tornado.locale.load_translations now accepts encodings other than UTF-8. UTF-16 and UTF-8 will be detected automatically if a BOM is present; for other encodings load_translations has an encoding parameter.

tornado.locks

• Lock and Semaphore now support the async with statement on Python 3.5.

tornado.options

• Dashes and underscores are now fully interchangeable in option names.

tornado.queues

• Queue now supports the async with statement on Python 3.5.

tornado.template

• tornado.template.ParseError now includes the filename in addition to line number.
• Whitespace handling has become more configurable. The Loader constructor now has a whitespace argument, there is a new template_whitespace Application setting, and there is a new {% whitespace %} template directive. All of these options take a mode name defined in the tornado.template.filter_whitespace function. The default mode is single, which is the same behavior as prior versions of Tornado.

tornado.testing

• ExpectLog objects now have a boolean logged_stack attribute to make it easier to test whether an exception stack trace was logged.

tornado.web

• The hard limit of 4000 bytes per outgoing header has been removed.
• StaticFileHandler returns the correct Content-Type for files with .gz, .bz2, and .xz extensions.
• Responses smaller than 1000 bytes will no longer be compressed.
• The default gzip compression level is now 6 (was 9).