What’s new in Tornado 4.3

Nov 6, 2015

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. See the users’ guide for more.
The async/await keywords are also available when compiling with Cython in older versions of Python.

This will be the last release of Tornado to support Python 2.6 or 3.2. Note that PyPy3 will continue to be supported even though it implements a mix of Python 3.2 and 3.3 features.

Tornado has several new dependencies: ordereddict on Python 2.6, singledispatch on all Python versions prior to 3.4 (This was an optional dependency in prior versions of Tornado, and is now mandatory), and backports_abc>=0.4 on all versions prior to 3.5. These dependencies will be installed automatically when installing with pip or setup.py install. These dependencies will not be required when running on Google App Engine.
Binary wheels are provided for Python 3.5 on Windows (32 and 64 bit).

New method OAuth2Mixin.oauth2_request can be used to make authenticated requests with an access token.
Now compatible with callbacks that have been compiled with Cython.

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

Fixed parsing of multi-line headers.
allow_nonstandard_methods=True now bypasses body sanity checks, in the same way as in simple_httpclient.
The PATCH method now allows a body without allow_nonstandard_methods=True.

WaitIterator now supports the async for statement on Python 3.5.
@gen.coroutine can be applied to functions compiled with Cython. On python versions prior to 3.5, the backports_abc package must be installed for this functionality.
Multi and multi_future are deprecated and replaced by a unified function multi.

Requests containing both Content-Length and Transfer-Encoding will be treated as an error.

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.
IOLoop.add_callback is faster in the single-threaded case.
IOLoop.add_callback no longer raises an error when called on a closed IOLoop, but the callback will not be invoked.

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.
Improved error handling in read_until_close.
Logging is less noisy when an SSL server is port scanned.
EINTR is now handled on all reads.

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.

A new time-based log rotation mode is available with --log_rotate_mode=time, --log-rotate-when, and log-rotate-interval.

When following redirects, streaming_callback and header_callback will no longer be run on the redirect responses (only the final non-redirect).
Responses containing both Content-Length and Transfer-Encoding will be treated as an error.

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.
Non-ASCII filenames are now supported.

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

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).
Fixed a regression in Tornado 4.2.1 that broke StaticFileHandler with a path of /.
tornado.web.HTTPError is now copyable with the copy module.
The exception Finish now accepts an argument which will be passed to the method RequestHandler.finish.
New Application setting xsrf_cookie_kwargs can be used to set additional attributes such as secure or httponly on the XSRF cookie.
Application.listen now returns the HTTPServer it created.