python3.7新增的asyncio特性

asyncio
The asyncio module has received many new features, usability and performance improvements. Notable changes include:

The new provisional asyncio.run() function can be used to run a coroutine from synchronous code by automatically creating and destroying the event loop. (Contributed by Yury Selivanov in bpo-32314.)

asyncio gained support for contextvars. loop.call_soon(), loop.call_soon_threadsafe(), loop.call_later(), loop.call_at(), and Future.add_done_callback() have a new optional keyword-only context parameter. Tasks now track their context automatically. See PEP 567 for more details. (Contributed by Yury Selivanov in bpo-32436.)

The new asyncio.create_task() function has been added as a shortcut to asyncio.get_event_loop().create_task(). (Contributed by Andrew Svetlov in bpo-32311.)

The new loop.start_tls() method can be used to upgrade an existing connection to TLS. (Contributed by Yury Selivanov in bpo-23749.)

The new loop.sock_recv_into() method allows reading data from a socket directly into a provided buffer making it possible to reduce data copies. (Contributed by Antoine Pitrou in bpo-31819.)

The new asyncio.current_task() function returns the currently running Task instance, and the new asyncio.all_tasks() function returns a set of all existing Task instances in a given loop. The Task.current_task() and Task.all_tasks() methods have been deprecated. (Contributed by Andrew Svetlov in bpo-32250.)

The new provisional BufferedProtocol class allows implementing streaming protocols with manual control over the receive buffer. (Contributed by Yury Selivanov in bpo-32251.)

The new asyncio.get_running_loop() function returns the currently running loop, and raises a RuntimeError if no loop is running. This is in contrast with asyncio.get_event_loop(), which will create a new event loop if none is running. (Contributed by Yury Selivanov in bpo-32269.)

The new StreamWriter.wait_closed() coroutine method allows waiting until the stream writer is closed. The new StreamWriter.is_closing() method can be used to determine if the writer is closing. (Contributed by Andrew Svetlov in bpo-32391.)

The new loop.sock_sendfile() coroutine method allows sending files using os.sendfile when possible. (Contributed by Andrew Svetlov in bpo-32410.)

The new Future.get_loop() and Task.get_loop() methods return the instance of the loop on which a task or a future were created. Server.get_loop() allows doing the same for asyncio.Server objects. (Contributed by Yury Selivanov in bpo-32415 and Srinivas Reddy Thatiparthy in bpo-32418.)

It is now possible to control how instances of asyncio.Server begin serving. Previously, the server would start serving immediately when created. The new start_serving keyword argument to loop.create_server() and loop.create_unix_server(), as well as Server.start_serving(), and Server.serve_forever() can be used to decouple server instantiation and serving. The new Server.is_serving() method returns True if the server is serving. Server objects are now asynchronous context managers:

srv = await loop.create_server(...)

async with srv:
    # some code

# At this point, srv is closed and no longer accepts new connections.
(Contributed by Yury Selivanov in bpo-32662.)

Callback objects returned by loop.call_later() gained the new when() method which returns an absolute scheduled callback timestamp. (Contributed by Andrew Svetlov in bpo-32741.)

The loop.create_datagram_endpoint() method gained support for Unix sockets. (Contributed by Quentin Dawans in bpo-31245.)

The asyncio.open_connection(), asyncio.start_server() functions, loop.create_connection(), loop.create_server(), loop.create_accepted_socket() methods and their corresponding UNIX socket variants now accept the ssl_handshake_timeout keyword argument. (Contributed by Neil Aspinall in bpo-29970.)

The new Handle.cancelled() method returns True if the callback was cancelled. (Contributed by Marat Sharafutdinov in bpo-31943.)

The asyncio source has been converted to use the async/await syntax. (Contributed by Andrew Svetlov in bpo-32193.)

The new ReadTransport.is_reading() method can be used to determine the reading state of the transport. Additionally, calls to ReadTransport.resume_reading() and ReadTransport.pause_reading() are now idempotent. (Contributed by Yury Selivanov in bpo-32356.)

Loop methods which accept socket paths now support passing path-like objects. (Contributed by Yury Selivanov in bpo-32066.)

In asyncio TCP sockets on Linux are now created with TCP_NODELAY flag set by default. (Contributed by Yury Selivanov and Victor Stinner in bpo-27456.)

Exceptions occurring in cancelled tasks are no longer logged. (Contributed by Yury Selivanov in bpo-30508.)

New WindowsSelectorEventLoopPolicy and WindowsProactorEventLoopPolicy classes. (Contributed by Yury Selivanov in bpo-33792.)

Several asyncio APIs have been deprecated.