# What’s new in Tornado 6.2.0

## Jul 3, 2022

### Deprecation notice

- April 2023 update: Python 3.12 reversed some of the changes described below. In Tornado 6.3, `AsyncTestCase`, `AsyncHTTPTestCase`, and the behavior of the `IOLoop` constructor related to the `make_current` parameter are no longer deprecated.

- Python 3.10 has begun the process of significant changes to the APIs for managing the event loop. Calls to methods such as `asyncio.get_event_loop` may now raise `DeprecationWarning` if no event loop is running. This has significant impact on the patterns for initializing applications, and in particular invalidates patterns that have long been the norm in Tornado’s documentation and actual usage. In the future (with some as-yet-unspecified future version of Python), the old APIs will be removed. The new recommended pattern is to start the event loop with `asyncio.run`. More detailed migration guides will be coming in the future.

  - The `IOLoop` constructor is deprecated unless the `make_current=False` argument is used. Use `IOLoop.current` when the loop is already running instead.

  - `AsyncTestCase` (and `AsyncHTTPTestCase`) are deprecated. Use `unittest.IsolatedAsyncioTestCase` instead.

  - Multi-process `TCPServer.bind`/`TCPServer.start` is deprecated. See `TCPServer` docs for supported alternatives.

  - `AnyThreadEventLoopPolicy` is deprecated. This class controls the creation of the “current” event loop so it will be removed when that concept is no longer supported.

  - `IOLoop.make_current` and `IOLoop.clear_current` are deprecated. In the future the concept of a “current” event loop as distinct from one that is currently running will be removed.

- `TwistedResolver` and `CaresResolver` are deprecated and will be removed in Tornado 7.0.

### General changes

- The minimum supported Python version is now 3.7.

- Wheels are now published with the Python stable ABI (`abi3`) for compatibility across versions of Python.

- SSL certificate verification and hostname checks are now enabled by default in more places (primarily in client-side usage of `SSLIOStream`).

- Various improvements to type hints throughout the package.

- CI has moved from Travis and Appveyor to Github Actions.

### `tornado.gen`

- Fixed a bug in which `WaitIterator.current_index` could be incorrect.

- `tornado.gen.TimeoutError` is now an alias for `asyncio.TimeoutError`.

### `tornado.http1connection`

- `max_body_size` may now be set to zero to disallow a non-empty body.

- `Content-Encoding: gzip` is now recognized case-insensitively.

### `tornado.httpclient`

- `curl_httpclient` now supports non-ASCII (ISO-8859-1) header values, same as `simple_httpclient`.

### `tornado.ioloop`

- `PeriodicCallback` now understands coroutines and will not start multiple copies if a previous invocation runs too long.

- `PeriodicCallback` now accepts `datetime.timedelta` objects in addition to numbers of milliseconds.

- Avoid logging “Event loop is closed” during shutdown-related race conditions.

- Tornado no longer calls `logging.basicConfig` when starting an IOLoop; this has been unnecessary since Python 3.2 added a logger of last resort.

- The `IOLoop` constructor now accepts an `asyncio_loop` keyword argument to initialize with a specfied asyncio event loop.

- It is now possible to construct an `IOLoop` on one thread (with `make_current=False`) and start it on a different thread.

### `tornado.iostream`

- `SSLIOStream` now supports reading more than 2GB at a time.

- `IOStream.write` now supports typed `memoryview` objects.

### `tornado.locale`

- `load_gettext_translations` no longer logs errors when language directories exist but do not contain the expected file.

### `tornado.netutil`

- `is_valid_ip` no longer raises exceptions when the input is too long.

- The default resolver now uses the same methods (and thread pool) as `asyncio`.

### `tornado.tcpserver`

- `TCPServer.listen` now supports more arguments to pass through to `netutil.bind_sockets`.

### `tornado.testing`

- `bind_unused_port` now takes an optional `address` argument.

- Wrapped test methods now include the `__wrapped__` attribute.

### `tornado.web`

- When using a custom `StaticFileHandler` subclass, the `reset()` method is now called on this subclass instead of the base class.

- Improved handling of the `Accept-Language` header.

- `Application.listen` now supports more arguments to pass through to `netutil.bind_sockets`.

### `tornado.websocket`

- `WebSocketClientConnection.write_message` now accepts `dict` arguments for consistency with `WebSocketHandler.write_message`.

- `WebSocketClientConnection.write_message` now raises an exception as documented if the connection is already closed.