docs/releases/v5.0.0.rst
Highlights
- The focus of this release is improving integration with `asyncio`.
On Python 3, the `.IOLoop` is always a wrapper around the `asyncio`
event loop, and `asyncio.Future` and `asyncio.Task` are used instead
of their Tornado counterparts. This means that libraries based on
`asyncio` can be mixed relatively seamlessly with those using
Tornado. While care has been taken to minimize the disruption from
this change, code changes may be required for compatibility with
Tornado 5.0, as detailed in the following section.
- Tornado 5.0 supports Python 2.7.9+ and 3.4+. Python 2.7 and 3.4 are
deprecated and support for them will be removed in Tornado 6.0,
which will require Python 3.5+.
Backwards-compatibility notes
Python 3.3 is no longer supported.
Versions of Python 2.7 that predate the ssl module update are no
longer supported. (The ssl module was updated in version 2.7.9,
although in some distributions the updates are present in builds
with a lower version number. Tornado requires ssl.SSLContext,
ssl.create_default_context, and ssl.match_hostname)
Versions of Python 3.5 prior to 3.5.2 are no longer supported due to a change in the async iterator protocol in that version.
The trollius project (asyncio backported to Python 2) is no
longer supported.
tornado.concurrent.Future is now an alias for asyncio.Future
when running on Python 3. This results in a number of minor
behavioral changes:
.Future objects can only be created while there is a current
.IOLoopFuture.add_done_callback has changed.
tornado.concurrent.future_add_done_callback can be used to
make the behavior more like older versions of Tornado (but not
identical). Some of these changes are also present in the Python
2 version of tornado.concurrent.Future to minimize the
difference between Python 2 and 3.asyncio.Future.cancel. A canceled .Future can no longer have
its result set. Applications that handle ~asyncio.Future
objects directly may want to use
tornado.concurrent.future_set_result_unless_cancelled. In
native coroutines, cancellation will cause an exception to be
raised in the coroutine.exc_info and set_exc_info methods are no longer
present. Use tornado.concurrent.future_set_exc_info to replace
the latter, and raise the exception with
~asyncio.Future.result to replace the former.io_loop arguments to many Tornado functions have been removed.
Use .IOLoop.current() instead of passing .IOLoop objects
explicitly.
On Python 3, .IOLoop is always a wrapper around the asyncio
event loop. IOLoop.configure is effectively removed on Python 3
(for compatibility, it may be called to redundantly specify the
asyncio-backed .IOLoop)
.IOLoop.instance is now a deprecated alias for .IOLoop.current.
Applications that need the cross-thread communication behavior
facilitated by .IOLoop.instance should use their own global variable
instead.
Other notes
- The ``futures`` (`concurrent.futures` backport) package is now required
on Python 2.7.
- The ``certifi`` and ``backports.ssl-match-hostname`` packages are no
longer required on Python 2.7.
- Python 3.6 or higher is recommended, because it features more
efficient garbage collection of `asyncio.Future` objects.
`tornado.auth`
.GoogleOAuth2Mixin now uses a newer set of URLs.tornado.autoreload
- On Python 3, uses ``__main__.__spec`` to more reliably reconstruct
the original command line and avoid modifying ``PYTHONPATH``.
- The ``io_loop`` argument to `tornado.autoreload.start` has been removed.
`tornado.concurrent`
tornado.concurrent.Future is now an alias for asyncio.Future
when running on Python 3. See "Backwards-compatibility notes" for
more.Future no longer blocks while callbacks
are being run. Instead, the callbacks are scheduled on the next
.IOLoop iteration.tornado.concurrent.TracebackFuture has been
removed.tornado.concurrent.chain_future now works with all three kinds of
Futures (Tornado, asyncio, and concurrent.futures)io_loop argument to tornado.concurrent.run_on_executor has
been removed..future_set_result_unless_cancelled,
.future_set_exc_info, and .future_add_done_callback help mask
the difference between asyncio.Future and Tornado's previous
Future implementation.tornado.curl_httpclient
- Improved debug logging on Python 3.
- The ``time_info`` response attribute now includes ``appconnect`` in
addition to other measurements.
- Closing a `.CurlAsyncHTTPClient` now breaks circular references that
could delay garbage collection.
- The ``io_loop`` argument to the `.CurlAsyncHTTPClient` constructor
has been removed.
`tornado.gen`
~~~~~~~~~~~~~
- ``tornado.gen.TimeoutError`` is now an alias for
`tornado.util.TimeoutError`.
- Leak detection for ``Futures`` created by this module now attributes
them to their proper caller instead of the coroutine machinery.
- Several circular references that could delay garbage collection have
been broken up.
- On Python 3, `asyncio.Task` is used instead of the Tornado coroutine
runner. This improves compatibility with some `asyncio` libraries
and adds support for cancellation.
- The ``io_loop`` arguments to ``YieldFuture`` and `.with_timeout` have
been removed.
`tornado.httpclient`
~~~~~~~~~~~~~~~~~~~~
- The ``io_loop`` argument to all `.AsyncHTTPClient` constructors has
been removed.
`tornado.httpserver`
~~~~~~~~~~~~~~~~~~~~
- It is now possible for a client to reuse a connection after sending
a chunked request.
- If a client sends a malformed request, the server now responds with
a 400 error instead of simply closing the connection.
- ``Content-Length`` and ``Transfer-Encoding`` headers are no longer
sent with 1xx or 204 responses (this was already true of 304
responses).
- When closing a connection to a HTTP/1.1 client, the ``Connection:
close`` header is sent with the response.
- The ``io_loop`` argument to the `.HTTPServer` constructor has been
removed.
- If more than one ``X-Scheme`` or ``X-Forwarded-Proto`` header is
present, only the last is used.
`tornado.httputil`
~~~~~~~~~~~~~~~~~~
- The string representation of `.HTTPServerRequest` objects (which are
sometimes used in log messages) no longer includes the request
headers.
- New function `.qs_to_qsl` converts the result of
`urllib.parse.parse_qs` to name-value pairs.
`tornado.ioloop`
~~~~~~~~~~~~~~~~
- ``tornado.ioloop.TimeoutError`` is now an alias for
`tornado.util.TimeoutError`.
- `.IOLoop.instance` is now a deprecated alias for `.IOLoop.current`.
- `.IOLoop.install` and `.IOLoop.clear_instance` are deprecated.
- The ``IOLoop.initialized`` method has been removed.
- On Python 3, the `asyncio`-backed `.IOLoop` is always used and
alternative `.IOLoop` implementations cannot be configured.
`.IOLoop.current` and related methods pass through to
`asyncio.get_event_loop`.
- `~.IOLoop.run_sync` cancels its argument on a timeout. This
results in better stack traces (and avoids log messages about leaks)
in native coroutines.
- New methods `.IOLoop.run_in_executor` and
`.IOLoop.set_default_executor` make it easier to run functions in
other threads from native coroutines (since
`concurrent.futures.Future` does not support ``await``).
- ``PollIOLoop`` (the default on Python 2) attempts to detect misuse
of `.IOLoop` instances across `os.fork`.
- The ``io_loop`` argument to `.PeriodicCallback` has been removed.
- It is now possible to create a `.PeriodicCallback` in one thread
and start it in another without passing an explicit event loop.
- The ``IOLoop.set_blocking_signal_threshold`` and
``IOLoop.set_blocking_log_threshold`` methods are deprecated because
they are not implemented for the `asyncio` event loop`. Use the
``PYTHONASYNCIODEBUG=1`` environment variable instead.
- `.IOLoop.clear_current` now works if it is called before any
current loop is established.
`tornado.iostream`
~~~~~~~~~~~~~~~~~~
- The ``io_loop`` argument to the `.IOStream` constructor has been removed.
- New method `.BaseIOStream.read_into` provides a minimal-copy alternative to
`.BaseIOStream.read_bytes`.
- `.BaseIOStream.write` is now much more efficient for very large amounts of data.
- Fixed some cases in which ``IOStream.error`` could be inaccurate.
- Writing a `memoryview` can no longer result in "BufferError:
Existing exports of data: object cannot be re-sized".
`tornado.locks`
~~~~~~~~~~~~~~~
- As a side effect of the ``Future`` changes, waiters are always
notified asynchronously with respect to `.Condition.notify`.
`tornado.netutil`
~~~~~~~~~~~~~~~~~
- The default `.Resolver` now uses `.IOLoop.run_in_executor`.
`.ExecutorResolver`, `.BlockingResolver`, and `.ThreadedResolver` are
deprecated.
- The ``io_loop`` arguments to `.add_accept_handler`,
`.ExecutorResolver`, and `.ThreadedResolver` have been removed.
- `.add_accept_handler` returns a callable which can be used to remove
all handlers that were added.
- `.OverrideResolver` now accepts per-family overrides.
`tornado.options`
~~~~~~~~~~~~~~~~~
- Duplicate option names are now detected properly whether they use
hyphens or underscores.
`tornado.platform.asyncio`
.AsyncIOLoop and .AsyncIOMainLoop are now used automatically
when appropriate; referencing them explicitly is no longer
recommended..IOLoop or making it current now also sets the
asyncio event loop for the current thread. Closing an .IOLoop
closes the corresponding asyncio event loop..to_tornado_future and .to_asyncio_future are deprecated since
they are now no-ops.~.AnyThreadEventLoopPolicy can now be used to easily allow the creation
of event loops on any thread (similar to Tornado's prior policy).tornado.platform.caresresolver
- The ``io_loop`` argument to `.CaresResolver` has been removed.
`tornado.platform.twisted`
~~~~~~~~~~~~~~~~~~~~~~~~~~
- The ``io_loop`` arguments to ``TornadoReactor``, ``TwistedResolver``,
and ``tornado.platform.twisted.install`` have been removed.
`tornado.process`
~~~~~~~~~~~~~~~~~
- The ``io_loop`` argument to the `.Subprocess` constructor and
`.Subprocess.initialize` has been removed.
`tornado.routing`
~~~~~~~~~~~~~~~~~
- A default 404 response is now generated if no delegate is found for
a request.
`tornado.simple_httpclient`
~~~~~~~~~~~~~~~~~~~~~~~~~~~
- The ``io_loop`` argument to `.SimpleAsyncHTTPClient` has been removed.
- TLS is now configured according to `ssl.create_default_context` by
default.
`tornado.tcpclient`
~~~~~~~~~~~~~~~~~~~
- The ``io_loop`` argument to the `.TCPClient` constructor has been
removed.
- `.TCPClient.connect` has a new ``timeout`` argument.
`tornado.tcpserver`
~~~~~~~~~~~~~~~~~~~
- The ``io_loop`` argument to the `.TCPServer` constructor has been
removed.
- `.TCPServer` no longer logs ``EBADF`` errors during shutdown.
`tornado.testing`
~~~~~~~~~~~~~~~~~
- The deprecated ``tornado.testing.get_unused_port`` and
``tornado.testing.LogTrapTestCase`` have been removed.
- `.AsyncHTTPTestCase.fetch` now supports absolute URLs.
- `.AsyncHTTPTestCase.fetch` now connects to ``127.0.0.1``
instead of ``localhost`` to be more robust against faulty
ipv6 configurations.
`tornado.util`
~~~~~~~~~~~~~~
- `tornado.util.TimeoutError` replaces ``tornado.gen.TimeoutError``
and ``tornado.ioloop.TimeoutError``.
- `.Configurable` now supports configuration at multiple levels of an
inheritance hierarchy.
`tornado.web`
~~~~~~~~~~~~~
- `.RequestHandler.set_status` no longer requires that the given
status code appear in `http.client.responses`.
- It is no longer allowed to send a body with 1xx or 204 responses.
- Exception handling now breaks up reference cycles that could delay
garbage collection.
- `.RedirectHandler` now copies any query arguments from the request
to the redirect location.
- If both ``If-None-Match`` and ``If-Modified-Since`` headers are present
in a request to `.StaticFileHandler`, the latter is now ignored.
`tornado.websocket`
~~~~~~~~~~~~~~~~~~~
- The C accelerator now operates on multiple bytes at a time to
improve performance.
- Requests with invalid websocket headers now get a response with
status code 400 instead of a closed connection.
- `.WebSocketHandler.write_message` now raises `.WebSocketClosedError` if
the connection closes while the write is in progress.
- The ``io_loop`` argument to `.websocket_connect` has been removed.