What’s new in Tornado 3.0
Mar 29, 2013
Highlights
- The callback argument to many asynchronous methods is now
optional, and these methods return a Future. The tornado.gen
module now understands Futures, and these methods can be used
directly without a gen.Task wrapper.
- New function IOLoop.current returns the IOLoop that is running
on the current thread (as opposed to IOLoop.instance, which
returns a specific thread’s (usually the main thread’s) IOLoop.
- New class tornado.netutil.Resolver provides an asynchronous
interface to DNS resolution. The default implementation is still
blocking, but non-blocking implementations are available using one
of three optional dependencies: ThreadedResolver
using the concurrent.futures thread pool,
tornado.platform.caresresolver.CaresResolver using the pycares
library, or tornado.platform.twisted.TwistedResolver using twisted
- Tornado’s logging is now less noisy, and it no longer goes directly
to the root logger, allowing for finer-grained configuration.
- New class tornado.process.Subprocess wraps subprocess.Popen with
PipeIOStream access to the child’s file descriptors.
- IOLoop now has a static configure
method like the one on AsyncHTTPClient, which can be used to
select an IOLoop implementation other than the default.
- IOLoop can now optionally use a monotonic clock if available
(see below for more details).
Backwards-incompatible changes
- Python 2.5 is no longer supported. Python 3 is now supported in a single
codebase instead of using 2to3
- The tornado.database module has been removed. It is now available
as a separate package, torndb
- Functions that take an io_loop parameter now default to
IOLoop.current() instead of IOLoop.instance().
- Empty HTTP request arguments are no longer ignored. This applies to
HTTPRequest.arguments and RequestHandler.get_argument[s]
in WSGI and non-WSGI modes.
- On Python 3, tornado.escape.json_encode no longer accepts byte strings.
- On Python 3, the get_authenticated_user methods in tornado.auth
now return character strings instead of byte strings.
- tornado.netutil.TCPServer has moved to its own module,
tornado.tcpserver.
- The Tornado test suite now requires unittest2 when run on Python 2.6.
- tornado.options.options is no longer a subclass of dict; attribute-style
access is now required.
Detailed changes by module
Multiple modules
- Tornado no longer logs to the root logger. Details on the new logging
scheme can be found under the tornado.log module. Note that in some
cases this will require that you add an explicit logging configuration
in order to see any output (perhaps just calling logging.basicConfig()),
although both IOLoop.start() and tornado.options.parse_command_line
will do this for you.
- On python 3.2+, methods that take an ssl_options argument (on
SSLIOStream, TCPServer, and HTTPServer) now accept either a
dictionary of options or an ssl.SSLContext object.
- New optional dependency on concurrent.futures to provide better support
for working with threads. concurrent.futures is in the standard library
for Python 3.2+, and can be installed on older versions with
pip install futures.
- tornado.autoreload is now more reliable when there are errors at import
time.
- Calling tornado.autoreload.start (or creating an Application with
debug=True) twice on the same IOLoop now does nothing (instead of
creating multiple periodic callbacks). Starting autoreload on
more than one IOLoop in the same process now logs a warning.
- Scripts run by autoreload no longer inherit __future__ imports
used by Tornado.
- On Python 3, the get_authenticated_user method family now returns
character strings instead of byte strings.
- Asynchronous methods defined in tornado.auth now return a
Future, and their callback argument is optional. The
Future interface is preferred as it offers better error handling
(the previous interface just logged a warning and returned None).
- The tornado.auth mixin classes now define a method
get_auth_http_client, which can be overridden to use a non-default
AsyncHTTPClient instance (e.g. to use a different IOLoop)
- Subclasses of OAuthMixin are encouraged to override
OAuthMixin._oauth_get_user_future instead of _oauth_get_user,
although both methods are still supported.
tornado.curl_httpclient
- Preliminary support for tornado.curl_httpclient on Python 3. The latest
official release of pycurl only supports Python 2, but Ubuntu has a
port available in 12.10 (apt-get install python3-pycurl). This port
currently has bugs that prevent it from handling arbitrary binary data
but it should work for textual (utf8) resources.
- Fix a crash with libcurl 7.29.0 if a curl object is created and closed
without being used.
- On Python 3, json_encode no longer accepts byte strings.
This mirrors the behavior of the underlying json module. Python 2 behavior
is unchanged but should be faster.
- New decorator @gen.coroutine is available as an alternative to
@gen.engine. It automatically returns a
Future, and within the function instead of
calling a callback you return a value with raise
gen.Return(value) (or simply return value in Python 3.3).
- Generators may now yield Future objects.
- Callbacks produced by gen.Callback and gen.Task are now automatically
stack-context-wrapped, to minimize the risk of context leaks when used
with asynchronous functions that don’t do their own wrapping.
- Fixed a memory leak involving generators, RequestHandler.flush,
and clients closing connections while output is being written.
- Yielding a large list no longer has quadratic performance.
- AsyncHTTPClient.fetch now returns a Future and its callback argument
is optional. When the future interface is used, any error will be raised
automatically, as if HTTPResponse.rethrow was called.
- AsyncHTTPClient.configure and all AsyncHTTPClient constructors
now take a defaults keyword argument. This argument should be a
dictionary, and its values will be used in place of corresponding
attributes of HTTPRequest that are not set.
- All unset attributes of tornado.httpclient.HTTPRequest are now
None. The default values of some attributes
(connect_timeout, request_timeout, follow_redirects,
max_redirects, use_gzip, proxy_password,
allow_nonstandard_methods, and validate_cert have been moved
from HTTPRequest to the client
implementations.
- The max_clients argument to AsyncHTTPClient is now a keyword-only
argument.
- Keyword arguments to AsyncHTTPClient.configure are no longer used
when instantiating an implementation subclass directly.
- Secondary AsyncHTTPClient callbacks (streaming_callback,
header_callback, and prepare_curl_callback) now respect
StackContext.
- HTTPServer no longer logs an error when it is unable to read a second
request from an HTTP 1.1 keep-alive connection.
- HTTPServer now takes a protocol keyword argument which can be set
to https if the server is behind an SSL-decoding proxy that does not
set any supported X-headers.
- tornado.httpserver.HTTPConnection now has a set_close_callback
method that should be used instead of reaching into its stream
attribute.
- Empty HTTP request arguments are no longer ignored. This applies to
HTTPRequest.arguments and RequestHandler.get_argument[s]
in WSGI and non-WSGI modes.
- New function IOLoop.current returns the IOLoop that is running
on the current thread (as opposed to IOLoop.instance, which returns a
specific thread’s (usually the main thread’s) IOLoop).
- New method IOLoop.add_future to run a callback on the IOLoop when
an asynchronous Future finishes.
- IOLoop now has a static configure
method like the one on AsyncHTTPClient, which can be used to
select an IOLoop implementation other than the default.
- The IOLoop poller implementations (select, epoll, kqueue)
are now available as distinct subclasses of IOLoop. Instantiating
IOLoop will continue to automatically choose the best available
implementation.
- The IOLoop constructor has a new keyword argument time_func,
which can be used to set the time function used when scheduling callbacks.
This is most useful with the time.monotonic function, introduced
in Python 3.3 and backported to older versions via the monotime
module. Using a monotonic clock here avoids problems when the system
clock is changed.
- New function IOLoop.time returns the current time according to the
IOLoop. To use the new monotonic clock functionality, all calls to
IOLoop.add_timeout must be either pass a datetime.timedelta or
a time relative to IOLoop.time, not time.time. (time.time will
continue to work only as long as the IOLoop’s time_func argument
is not used).
- New convenience method IOLoop.run_sync can be used to start an IOLoop
just long enough to run a single coroutine.
- New method IOLoop.add_callback_from_signal is safe to use in a signal
handler (the regular add_callback method may deadlock).
- IOLoop now uses signal.set_wakeup_fd where available (Python 2.6+
on Unix) to avoid a race condition that could result in Python signal
handlers being delayed.
- Method IOLoop.running() has been removed.
- IOLoop has been refactored to better support subclassing.
- IOLoop.add_callback and add_callback_from_signal now take
*args, **kwargs to pass along to the callback.
- IOStream.connect now has an optional server_hostname argument
which will be used for SSL certificate validation when applicable.
Additionally, when supported (on Python 3.2+), this hostname
will be sent via SNI (and this is supported by tornado.simple_httpclient)
- Much of IOStream has been refactored into a separate class
BaseIOStream.
- New class tornado.iostream.PipeIOStream provides the IOStream
interface on pipe file descriptors.
- IOStream now raises a new exception
tornado.iostream.StreamClosedError when you attempt to read or
write after the stream has been closed (by either side).
- IOStream now simply closes the connection when it gets an
ECONNRESET error, rather than logging it as an error.
- IOStream.error no longer picks up unrelated exceptions.
- BaseIOStream.close now has an exc_info argument (similar to the
one used in the logging module) that can be used to set the stream’s
error attribute when closing it.
- BaseIOStream.read_until_close now works correctly when it is called
while there is buffered data.
- Fixed a major performance regression when run on PyPy (introduced in
Tornado 2.3).
tornado.simple_httpclient
- SimpleAsyncHTTPClient now takes a resolver keyword argument
(which may be passed to either the constructor or configure), to allow it to use the new non-blocking
tornado.netutil.Resolver.
- When following redirects, SimpleAsyncHTTPClient now treats a 302
response code the same as a 303. This is contrary to the HTTP spec
but consistent with all browsers and other major HTTP clients
(including CurlAsyncHTTPClient).
- The behavior of header_callback with SimpleAsyncHTTPClient has
changed and is now the same as that of CurlAsyncHTTPClient. The
header callback now receives the first line of the response (e.g.
HTTP/1.0 200 OK) and the final empty line.
- tornado.simple_httpclient now accepts responses with a 304
status code that include a Content-Length header.
- Fixed a bug in which SimpleAsyncHTTPClient callbacks were being run in the
client’s stack_context.
- stack_context.wrap now runs the wrapped callback in a more consistent
environment by recreating contexts even if they already exist on the
stack.
- Fixed a bug in which stack contexts could leak from one callback
chain to another.
- Yield statements inside a with statement can cause stack
contexts to become inconsistent; an exception will now be raised
when this case is detected.
- Errors while rendering templates no longer log the generated code,
since the enhanced stack traces (from version 2.1) should make this
unnecessary.
- The {% apply %} directive now works properly with functions that return
both unicode strings and byte strings (previously only byte strings were
supported).
- Code in templates is no longer affected by Tornado’s __future__ imports
(which previously included absolute_import and division).
tornado.util
- tornado.util.b (which was only intended for internal use) is gone.
- RequestHandler.set_header now overwrites previous header values
case-insensitively.
- tornado.web.RequestHandler has new attributes path_args and
path_kwargs, which contain the positional and keyword arguments
that are passed to the get/post/etc method. These attributes
are set before those methods are called, so they are available during
prepare()
- tornado.web.ErrorHandler no longer requires XSRF tokens on POST
requests, so posts to an unknown url will always return 404 instead of
complaining about XSRF tokens.
- Several methods related to HTTP status codes now take a reason keyword
argument to specify an alternate “reason” string (i.e. the “Not Found” in
“HTTP/1.1 404 Not Found”). It is now possible to set status codes other
than those defined in the spec, as long as a reason string is given.
- The Date HTTP header is now set by default on all responses.
- Etag/If-None-Match requests now work with StaticFileHandler.
- StaticFileHandler no longer sets Cache-Control: public unnecessarily.
- When gzip is enabled in a tornado.web.Application, appropriate
Vary: Accept-Encoding headers are now sent.
- It is no longer necessary to pass all handlers for a host in a single
Application.add_handlers call. Now the request will be matched
against the handlers for any host_pattern that includes the request’s
Host header.