事件循环 ¶

运行和停止循环 ¶

loop. run_until_complete ( future ) ¶

运行直到 future (实例化的 Future ) 已完成。

If the argument is a coroutine object it is implicitly scheduled to run as a asyncio.Task .

Return the Future’s result or raise its exception.

loop. run_forever ( ) ¶

Run the event loop until stop() 被调用。

若 stop() is called before run_forever() is called, the loop will poll the I/O selector once with a timeout of zero, run all callbacks scheduled in response to I/O events (and those that were already scheduled), and then exit.

若 stop() is called while run_forever() is running, the loop will run the current batch of callbacks and then exit. Note that new callbacks scheduled by callbacks will not run in this case; instead, they will run the next time run_forever() or run_until_complete() 被调用。

loop. stop ( ) ¶

Stop the event loop.

loop. is_running ( ) ¶

返回 True if the event loop is currently running.

loop. is_closed ( ) ¶

返回 True 若事件循环被关闭。

loop. close ( ) ¶

Close the event loop.

The loop must not be running when this function is called. Any pending callbacks will be discarded.

This method clears all queues and shuts down the executor, but does not wait for the executor to finish.

This method is idempotent and irreversible. No other methods should be called after the event loop is closed.

coroutine loop. shutdown_asyncgens ( ) ¶

Schedule all currently open 异步生成器 objects to close with an aclose() call. After calling this method, the event loop will issue a warning if a new asynchronous generator is iterated. This should be used to reliably finalize all scheduled asynchronous generators.

Note that there is no need to call this function when asyncio.run() 被使用。

范例：

try:
    loop.run_forever()
finally:
    loop.run_until_complete(loop.shutdown_asyncgens())
    loop.close()
											

3.6 版新增。

coroutine loop. shutdown_default_executor ( ) ¶

Schedule the closure of the default executor and wait for it to join all of the threads in the ThreadPoolExecutor . After calling this method, a RuntimeError 会被引发若 loop.run_in_executor() is called while using the default executor.

Note that there is no need to call this function when asyncio.run() 被使用。

3.9 版新增。

调度回调 ¶

loop. call_soon ( callback , *args , context=None ) ¶

Schedule the callback callback to be called with args arguments at the next iteration of the event loop.

Callbacks are called in the order in which they are registered. Each callback will be called exactly once.

An optional keyword-only context argument allows specifying a custom contextvars.Context 为 callback to run in. The current context is used when no context is provided.

实例化的 asyncio.Handle is returned, which can be used later to cancel the callback.

This method is not thread-safe.

loop. call_soon_threadsafe ( callback , *args , context=None ) ¶

A thread-safe variant of call_soon() . Must be used to schedule callbacks from another thread .

引发 RuntimeError if called on a loop that’s been closed. This can happen on a secondary thread when the main application is shutting down.

见 并发和多线程 section of the documentation.

# will schedule "print("Hello", flush=True)"
loop.call_soon(
    functools.partial(print, "Hello", flush=True))
										

调度延迟回调 ¶

Event loop provides mechanisms to schedule callback functions to be called at some point in the future. Event loop uses monotonic clocks to track time.

loop. call_later ( delay , callback , *args , context=None ) ¶

Schedule callback to be called after the given delay number of seconds (can be either an int or a float).

实例化的 asyncio.TimerHandle is returned which can be used to cancel the callback.

callback will be called exactly once. If two callbacks are scheduled for exactly the same time, the order in which they are called is undefined.

The optional positional args will be passed to the callback when it is called. If you want the callback to be called with keyword arguments use functools.partial() .

An optional keyword-only context argument allows specifying a custom contextvars.Context 为 callback to run in. The current context is used when no context is provided.

3.7 版改变： context keyword-only parameter was added. See PEP 567 了解更多细节。

3.8 版改变： In Python 3.7 and earlier with the default event loop implementation, the delay could not exceed one day. This has been fixed in Python 3.8.

loop. call_at ( when , callback , *args , context=None ) ¶

Schedule callback to be called at the given absolute timestamp when (an int or a float), using the same time reference as loop.time() .

This method’s behavior is the same as call_later() .

实例化的 asyncio.TimerHandle is returned which can be used to cancel the callback.

3.7 版改变： context keyword-only parameter was added. See PEP 567 了解更多细节。

3.8 版改变： In Python 3.7 and earlier with the default event loop implementation, the difference between when and the current time could not exceed one day. This has been fixed in Python 3.8.

loop. time ( ) ¶

Return the current time, as a float value, according to the event loop’s internal monotonic clock.

Creating Futures and Tasks ¶

loop. create_future ( ) ¶

创建 asyncio.Future object attached to the event loop.

This is the preferred way to create Futures in asyncio. This lets third-party event loops provide alternative implementations of the Future object (with better performance or instrumentation).

3.5.2 版新增。

loop. create_task ( coro , * , name=None ) ¶

Schedule the execution of a 协程 。返回 Task 对象。

Third-party event loops can use their own subclass of Task for interoperability. In this case, the result type is a subclass of Task .

若 name argument is provided and not None , it is set as the name of the task using Task.set_name() .

3.8 版改变： 添加 name 参数。

loop. set_task_factory ( factory ) ¶

Set a task factory that will be used by loop.create_task() .

若 factory is None the default task factory will be set. Otherwise, factory 必须是 callable with the signature matching (loop, coro) ，其中 loop is a reference to the active event loop, and coro is a coroutine object. The callable must return a asyncio.Future -compatible object.

loop. get_task_factory ( ) ¶

返回任务工厂或 None if the default one is in use.

打开网络连接 ¶

coroutine loop. create_connection ( protocol_factory , host=None , port=None , * , ssl=None , family=0 , proto=0 , flags=0 , sock=None , local_addr=None , server_hostname=None , ssl_handshake_timeout=None , happy_eyeballs_delay=None , interleave=None ) ¶

Open a streaming transport connection to a given address specified by host and port .

套接字族可以是 AF_INET or AF_INET6 从属 host (或 系列 自变量，若提供)。

套接字类型将是 SOCK_STREAM .

protocol_factory must be a callable returning an asyncio protocol 实现。

This method will try to establish the connection in the background. When successful, it returns a (transport, protocol) 对。

The chronological synopsis of the underlying operation is as follows:

1. The connection is established and a transport is created for it.

2. protocol_factory is called without arguments and is expected to return a protocol 实例。

3. The protocol instance is coupled with the transport by calling its connection_made() 方法。

4. A (transport, protocol) tuple is returned on success.

The created transport is an implementation-dependent bidirectional stream.

其它自变量：

• ssl : if given and not false, a SSL/TLS transport is created (by default a plain TCP transport is created). If ssl 是 ssl.SSLContext object, this context is used to create the transport; if ssl is True , a default context returned from ssl.create_default_context() 被使用。

  另请参阅

  SSL/TLS 安全注意事项

• server_hostname sets or overrides the hostname that the target server’s certificate will be matched against. Should only be passed if ssl 不是 None . By default the value of the host argument is used. If host is empty, there is no default and you must pass a value for server_hostname 。若 server_hostname is an empty string, hostname matching is disabled (which is a serious security risk, allowing for potential man-in-the-middle attacks).

• 系列 , proto , flags are the optional address family, protocol and flags to be passed through to getaddrinfo() for host resolution. If given, these should all be integers from the corresponding socket module constants.

• happy_eyeballs_delay , if given, enables Happy Eyeballs for this connection. It should be a floating-point number representing the amount of time in seconds to wait for a connection attempt to complete, before starting the next attempt in parallel. This is the “Connection Attempt Delay” as defined in RFC 8305 . A sensible default value recommended by the RFC is 0.25 (250 milliseconds).

• interleave controls address reordering when a host name resolves to multiple IP addresses. If 0 or unspecified, no reordering is done, and addresses are tried in the order returned by getaddrinfo() . If a positive integer is specified, the addresses are interleaved by address family, and the given integer is interpreted as “First Address Family Count” as defined in RFC 8305 。默认为 0 if happy_eyeballs_delay is not specified, and 1 if it is.

• sock , if given, should be an existing, already connected socket.socket object to be used by the transport. If sock is given, none of host , port , 系列 , proto , flags , happy_eyeballs_delay , interleave and local_addr should be specified.

• local_addr ，若给定，是 (local_host, local_port) tuple used to bind the socket locally. The local_host and local_port are looked up using getaddrinfo() , similarly to host and port .

• ssl_handshake_timeout is (for a TLS connection) the time in seconds to wait for the TLS handshake to complete before aborting the connection. 60.0 seconds if None (default).

3.8 版新增： 添加 happy_eyeballs_delay and interleave 参数。

Happy Eyeballs Algorithm: Success with Dual-Stack Hosts. When a server’s IPv4 path and protocol are working, but the server’s IPv6 path and protocol are not working, a dual-stack client application experiences significant connection delay compared to an IPv4-only client. This is undesirable because it causes the dual- stack client to have a worse user experience. This document specifies requirements for algorithms that reduce this user-visible delay and provides an algorithm.

更多信息： https://tools.ietf.org/html/rfc6555

3.7 版新增： ssl_handshake_timeout 参数。

3.6 版改变： 套接字选项 TCP_NODELAY is set by default for all TCP connections.

3.5 版改变： Added support for SSL/TLS in ProactorEventLoop .

另请参阅

open_connection() function is a high-level alternative API. It returns a pair of ( StreamReader , StreamWriter ) that can be used directly in async/await code.

coroutine loop. create_datagram_endpoint ( protocol_factory , local_addr=None , remote_addr=None , * , family=0 , proto=0 , flags=0 , reuse_address=None , reuse_port=None , allow_broadcast=None , sock=None ) ¶

注意

参数 reuse_address is no longer supported, as using SO_REUSEADDR poses a significant security concern for UDP. Explicitly passing reuse_address=True 会引发异常。

When multiple processes with differing UIDs assign sockets to an identical UDP socket address with SO_REUSEADDR , incoming packets can become randomly distributed among the sockets.

For supported platforms, reuse_port can be used as a replacement for similar functionality. With reuse_port , SO_REUSEPORT is used instead, which specifically prevents processes with differing UIDs from assigning sockets to the same socket address.

创建数据报连接。

套接字族可以是 AF_INET , AF_INET6 ，或 AF_UNIX ，从属 host (或 系列 自变量，若提供)。

套接字类型将是 SOCK_DGRAM .

protocol_factory must be a callable returning a protocol 实现。

元组 (transport, protocol) 被返回当成功时。

其它自变量：

• local_addr ，若给定，是 (local_host, local_port) tuple used to bind the socket locally. The local_host and local_port are looked up using getaddrinfo() .

• remote_addr ，若给定，是 (remote_host, remote_port) tuple used to connect the socket to a remote address. The remote_host and remote_port are looked up using getaddrinfo() .

• 系列 , proto , flags are the optional address family, protocol and flags to be passed through to getaddrinfo() for host resolution. If given, these should all be integers from the corresponding socket module constants.

• reuse_port tells the kernel to allow this endpoint to be bound to the same port as other existing endpoints are bound to, so long as they all set this flag when being created. This option is not supported on Windows and some Unixes. If the SO_REUSEPORT constant is not defined then this capability is unsupported.

• allow_broadcast tells the kernel to allow this endpoint to send messages to the broadcast address.

• sock can optionally be specified in order to use a preexisting, already connected, socket.socket object to be used by the transport. If specified, local_addr and remote_addr should be omitted (must be None ).

见 UDP echo client protocol and UDP echo server protocol 范例。

3.4.4 版改变： 系列 , proto , flags , reuse_address , reuse_port, *allow_broadcast ，和 sock 参数被添加。

3.8.1 版改变： reuse_address parameter is no longer supported due to security concerns.

3.8 版改变： 添加支持 Windows。

coroutine loop. create_unix_connection ( protocol_factory , path=None , * , ssl=None , sock=None , server_hostname=None , ssl_handshake_timeout=None ) ¶

Create a Unix connection.

The socket family will be AF_UNIX ; socket type will be SOCK_STREAM .

元组 (transport, protocol) 被返回当成功时。

path is the name of a Unix domain socket and is required, unless a sock parameter is specified. Abstract Unix sockets, str , bytes ，和 Path paths are supported.

See the documentation of the loop.create_connection() method for information about arguments to this method.

可用性 : Unix.

3.7 版新增： ssl_handshake_timeout 参数。

3.7 版改变： path parameter can now be a 像路径对象 .

创建网络服务器 ¶

coroutine loop. create_server ( protocol_factory , host=None , port=None , * , family=socket.AF_UNSPEC , flags=socket.AI_PASSIVE , sock=None , backlog=100 , ssl=None , reuse_address=None , reuse_port=None , ssl_handshake_timeout=None , start_serving=True ) ¶

Create a TCP server (socket type SOCK_STREAM ) listening on port 的 host 地址。

返回 Server 对象。

Arguments:

• protocol_factory must be a callable returning a protocol 实现。

• host parameter can be set to several types which determine where the server would be listening:

  • 若 host is a string, the TCP server is bound to a single network interface specified by host .

  • 若 host is a sequence of strings, the TCP server is bound to all network interfaces specified by the sequence.

  • 若 host is an empty string or None , all interfaces are assumed and a list of multiple sockets will be returned (most likely one for IPv4 and another one for IPv6).

• 系列 can be set to either socket.AF_INET or AF_INET6 to force the socket to use IPv4 or IPv6. If not set, the 系列 will be determined from host name (defaults to AF_UNSPEC ).

• flags is a bitmask for getaddrinfo() .

• sock can optionally be specified in order to use a preexisting socket object. If specified, host and port must not be specified.

• backlog is the maximum number of queued connections passed to listen() (defaults to 100).

• ssl can be set to an SSLContext instance to enable TLS over the accepted connections.

• reuse_address tells the kernel to reuse a local socket in TIME_WAIT state, without waiting for its natural timeout to expire. If not specified will automatically be set to True 在 Unix。

• reuse_port tells the kernel to allow this endpoint to be bound to the same port as other existing endpoints are bound to, so long as they all set this flag when being created. This option is not supported on Windows.

• ssl_handshake_timeout is (for a TLS server) the time in seconds to wait for the TLS handshake to complete before aborting the connection. 60.0 seconds if None (default).

• start_serving 设为 True (the default) causes the created server to start accepting connections immediately. When set to False , the user should await on Server.start_serving() or Server.serve_forever() to make the server to start accepting connections.

3.7 版新增： 添加 ssl_handshake_timeout and start_serving 参数。

3.6 版改变： 套接字选项 TCP_NODELAY is set by default for all TCP connections.

3.5 版改变： Added support for SSL/TLS in ProactorEventLoop .

3.5.1 版改变： host parameter can be a sequence of strings.

另请参阅

start_server() function is a higher-level alternative API that returns a pair of StreamReader and StreamWriter that can be used in an async/await code.

coroutine loop. create_unix_server ( protocol_factory , path=None , * , sock=None , backlog=100 , ssl=None , ssl_handshake_timeout=None , start_serving=True ) ¶

类似 loop.create_server() but works with the AF_UNIX socket family.

path is the name of a Unix domain socket, and is required, unless a sock argument is provided. Abstract Unix sockets, str , bytes ，和 Path paths are supported.

See the documentation of the loop.create_server() method for information about arguments to this method.

可用性 : Unix.

3.7 版新增： ssl_handshake_timeout and start_serving 参数。

3.7 版改变： path parameter can now be a Path 对象。

coroutine loop. connect_accepted_socket ( protocol_factory , sock , * , ssl=None , ssl_handshake_timeout=None ) ¶

Wrap an already accepted connection into a transport/protocol pair.

This method can be used by servers that accept connections outside of asyncio but that use asyncio to handle them.

参数：

• protocol_factory must be a callable returning a protocol 实现。

• sock is a preexisting socket object returned from socket.accept .

• ssl can be set to an SSLContext to enable SSL over the accepted connections.

• ssl_handshake_timeout is (for an SSL connection) the time in seconds to wait for the SSL handshake to complete before aborting the connection. 60.0 seconds if None (default).

返回 (transport, protocol) 对。

3.7 版新增： ssl_handshake_timeout 参数。

3.5.3 版新增。

传输文件 ¶

coroutine loop. sendfile ( transport , file , offset=0 , count=None , * , fallback=True ) ¶

发送 file over a transport . Return the total number of bytes sent.

The method uses high-performance os.sendfile() if available.

file must be a regular file object opened in binary mode.

offset tells from where to start reading the file. If specified, count is the total number of bytes to transmit as opposed to sending the file until EOF is reached. File position is always updated, even when this method raises an error, and file.tell() can be used to obtain the actual number of bytes sent.

fallback 设为 True makes asyncio to manually read and send the file when the platform does not support the sendfile system call (e.g. Windows or SSL socket on Unix).

引发 SendfileNotAvailableError if the system does not support the sendfile syscall and fallback is False .

3.7 版新增。

TLS 升级 ¶

coroutine loop. start_tls ( transport , protocol , sslcontext , * , server_side=False , server_hostname=None , ssl_handshake_timeout=None ) ¶

Upgrade an existing transport-based connection to TLS.

Return a new transport instance, that the protocol must start using immediately after the await 。 transport instance passed to the start_tls method should never be used again.

参数：

• transport and protocol instances that methods like create_server() and create_connection() return.

• sslcontext : a configured instance of SSLContext .

• server_side pass True when a server-side connection is being upgraded (like the one created by create_server() ).

• server_hostname : sets or overrides the host name that the target server’s certificate will be matched against.

• ssl_handshake_timeout is (for a TLS connection) the time in seconds to wait for the TLS handshake to complete before aborting the connection. 60.0 seconds if None (default).

3.7 版新增。

看守文件描述符 ¶

loop. add_reader ( fd , callback , *args ) ¶

Start monitoring the fd file descriptor for read availability and invoke callback with the specified arguments once fd is available for reading.

loop. remove_reader ( fd ) ¶

Stop monitoring the fd file descriptor for read availability.

loop. add_writer ( fd , callback , *args ) ¶

Start monitoring the fd file descriptor for write availability and invoke callback with the specified arguments once fd is available for writing.

使用 functools.partial() to pass keyword arguments to callback .

loop. remove_writer ( fd ) ¶

Stop monitoring the fd file descriptor for write availability.

另请参阅 平台支持 section for some limitations of these methods.

直接操控套接字对象 ¶

In general, protocol implementations that use transport-based APIs such as loop.create_connection() and loop.create_server() are faster than implementations that work with sockets directly. However, there are some use cases when performance is not critical, and working with socket objects directly is more convenient.

coroutine loop. sock_recv ( sock , nbytes ) ¶

接收直到 nbytes from sock . Asynchronous version of socket.recv() .

Return the received data as a bytes object.

sock 必须是非阻塞套接字。

3.7 版改变： Even though this method was always documented as a coroutine method, releases before Python 3.7 returned a Future . Since Python 3.7 this is an async def 方法。

coroutine loop. sock_recv_into ( sock , buf ) ¶

Receive data from sock into the buf buffer. Modeled after the blocking socket.recv_into() 方法。

Return the number of bytes written to the buffer.

sock 必须是非阻塞套接字。

3.7 版新增。

coroutine loop. sock_sendall ( sock , data ) ¶

发送 data 到 sock 套接字。异步版本的 socket.sendall() .

This method continues to send to the socket until either all data in data has been sent or an error occurs. None is returned on success. On error, an exception is raised. Additionally, there is no way to determine how much data, if any, was successfully processed by the receiving end of the connection.

sock 必须是非阻塞套接字。

3.7 版改变： Even though the method was always documented as a coroutine method, before Python 3.7 it returned an Future . Since Python 3.7, this is an async def 方法。

coroutine loop. sock_connect ( sock , address ) ¶

Connect sock to a remote socket at address .

Asynchronous version of socket.connect() .

sock 必须是非阻塞套接字。

3.5.2 版改变： address no longer needs to be resolved. sock_connect will try to check if the address is already resolved by calling socket.inet_pton() . If not, loop.getaddrinfo() will be used to resolve the address .

另请参阅

loop.create_connection() and asyncio.open_connection() .

coroutine loop. sock_accept ( sock ) ¶

Accept a connection. Modeled after the blocking socket.accept() 方法。

The socket must be bound to an address and listening for connections. The return value is a pair (conn, address) where conn 是 new 套接字对象用于发送和接收数据当连接上时，和 address 是绑定到连接另一端的套接字地址。

sock 必须是非阻塞套接字。

3.7 版改变： Even though the method was always documented as a coroutine method, before Python 3.7 it returned a Future . Since Python 3.7, this is an async def 方法。

另请参阅

loop.create_server() and start_server() .

coroutine loop. sock_sendfile ( sock , file , offset=0 , count=None , * , fallback=True ) ¶

Send a file using high-performance os.sendfile if possible. Return the total number of bytes sent.

Asynchronous version of socket.sendfile() .

sock must be a non-blocking socket.SOCK_STREAM socket .

file must be a regular file object open in binary mode.

offset tells from where to start reading the file. If specified, count is the total number of bytes to transmit as opposed to sending the file until EOF is reached. File position is always updated, even when this method raises an error, and file.tell() can be used to obtain the actual number of bytes sent.

fallback , when set to True , makes asyncio manually read and send the file when the platform does not support the sendfile syscall (e.g. Windows or SSL socket on Unix).

引发 SendfileNotAvailableError if the system does not support sendfile syscall and fallback is False .

sock 必须是非阻塞套接字。

3.7 版新增。

DNS ¶

coroutine loop. getaddrinfo ( host , port , * , family=0 , type=0 , proto=0 , flags=0 ) ¶

Asynchronous version of socket.getaddrinfo() .

coroutine loop. getnameinfo ( sockaddr , flags=0 ) ¶

Asynchronous version of socket.getnameinfo() .

操控管道 ¶

coroutine loop. connect_read_pipe ( protocol_factory , pipe ) ¶

Register the read end of pipe in the event loop.

protocol_factory must be a callable returning an asyncio protocol 实现。

pipe 是 像文件对象 .

Return pair (transport, protocol) ，其中 transport 支持 ReadTransport interface and protocol is an object instantiated by the protocol_factory .

With SelectorEventLoop event loop, the pipe is set to non-blocking mode.

coroutine loop. connect_write_pipe ( protocol_factory , pipe ) ¶

Register the write end of pipe in the event loop.

protocol_factory must be a callable returning an asyncio protocol 实现。

pipe is 像文件对象 .

Return pair (transport, protocol) ，其中 transport supports WriteTransport interface and protocol is an object instantiated by the protocol_factory .

With SelectorEventLoop event loop, the pipe is set to non-blocking mode.

Unix 信号 ¶

loop. add_signal_handler ( signum , callback , *args ) ¶

Set callback as the handler for the signum 信号。

The callback will be invoked by loop , along with other queued callbacks and runnable coroutines of that event loop. Unlike signal handlers registered using signal.signal() , a callback registered with this function is allowed to interact with the event loop.

引发 ValueError if the signal number is invalid or uncatchable. Raise RuntimeError if there is a problem setting up the handler.

使用 functools.partial() to pass keyword arguments to callback .

像 signal.signal() , this function must be invoked in the main thread.

loop. remove_signal_handler ( sig ) ¶

Remove the handler for the sig 信号。

返回 True if the signal handler was removed, or False if no handler was set for the given signal.

可用性 : Unix.

在线程 (或进程池) 中执行代码 ¶

awaitable loop. run_in_executor ( executor , func , *args ) ¶

Arrange for func to be called in the specified executor.

executor argument should be an concurrent.futures.Executor instance. The default executor is used if executor is None .

范例：

import asyncio
import concurrent.futures
def blocking_io():
    # File operations (such as logging) can block the
    # event loop: run them in a thread pool.
    with open('/dev/urandom', 'rb') as f:
        return f.read(100)
def cpu_bound():
    # CPU-bound operations will block the event loop:
    # in general it is preferable to run them in a
    # process pool.
    return sum(i * i for i in range(10 ** 7))
async def main():
    loop = asyncio.get_running_loop()
    ## Options:
    # 1. Run in the default loop's executor:
    result = await loop.run_in_executor(
        None, blocking_io)
    print('default thread pool', result)
    # 2. Run in a custom thread pool:
    with concurrent.futures.ThreadPoolExecutor() as pool:
        result = await loop.run_in_executor(
            pool, blocking_io)
        print('custom thread pool', result)
    # 3. Run in a custom process pool:
    with concurrent.futures.ProcessPoolExecutor() as pool:
        result = await loop.run_in_executor(
            pool, cpu_bound)
        print('custom process pool', result)
asyncio.run(main())
											

此方法返回 asyncio.Future 对象。

使用 functools.partial() to pass keyword arguments to func .

3.5.3 版改变： loop.run_in_executor() no longer configures the max_workers of the thread pool executor it creates, instead leaving it up to the thread pool executor ( ThreadPoolExecutor ) to set the default.

loop. set_default_executor ( executor ) ¶

Set executor as the default executor used by run_in_executor() . executor should be an instance of ThreadPoolExecutor .

从 3.8 版起弃用： Using an executor that is not an instance of ThreadPoolExecutor is deprecated and will trigger an error in Python 3.9.

executor 必须是实例化的 concurrent.futures.ThreadPoolExecutor .

错误处理 API ¶

Allows customizing how exceptions are handled in the event loop.

loop. set_exception_handler ( handler ) ¶

Set handler as the new event loop exception handler.

若 handler is None , the default exception handler will be set. Otherwise, handler must be a callable with the signature matching (loop, context) ，其中 loop is a reference to the active event loop, and context 是 dict object containing the details of the exception (see call_exception_handler() documentation for details about context).

loop. get_exception_handler ( ) ¶

返回当前异常处理程序，或 None if no custom exception handler was set.

3.5.2 版新增。

loop. default_exception_handler ( context ) ¶

默认异常处理程序。

This is called when an exception occurs and no exception handler is set. This can be called by a custom exception handler that wants to defer to the default handler behavior.

context parameter has the same meaning as in call_exception_handler() .

loop. call_exception_handler ( context ) ¶

Call the current event loop exception handler.

context 是 dict object containing the following keys (new keys may be introduced in future Python versions):

• ‘message’: Error message;

• ‘exception’ (optional): Exception object;

• ‘future’ (optional): asyncio.Future 实例；

• ‘handle’ (optional): asyncio.Handle 实例；

• ‘protocol’ (optional): Protocol 实例；

• ‘transport’ (optional): Transport 实例；

• ‘socket’ (optional): socket.socket 实例。

注意

This method should not be overloaded in subclassed event loops. For custom exception handling, use the set_exception_handler() 方法。

启用调试模式 ¶

loop. get_debug ( ) ¶

获取调试模式 ( bool ) of the event loop.

默认值为 True if the environment variable PYTHONASYNCIODEBUG is set to a non-empty string, False 否则。

loop. set_debug ( enabled: bool ) ¶

Set the debug mode of the event loop.

3.7 版改变： 新的 Python 开发模式 can now also be used to enable the debug mode.

运行子进程 ¶

Methods described in this subsections are low-level. In regular async/await code consider using the high-level asyncio.create_subprocess_shell() and asyncio.create_subprocess_exec() convenience functions instead.

coroutine loop. subprocess_exec ( protocol_factory , *args , stdin=subprocess.PIPE , stdout=subprocess.PIPE , stderr=subprocess.PIPE , **kwargs ) ¶

Create a subprocess from one or more string arguments specified by args .

args must be a list of strings represented by:

• str ;

• or bytes , encoded to the 文件系统编码 .

The first string specifies the program executable, and the remaining strings specify the arguments. Together, string arguments form the argv of the program.

This is similar to the standard library subprocess.Popen class called with shell=False and the list of strings passed as the first argument; however, where Popen takes a single argument which is list of strings, subprocess_exec takes multiple string arguments.

protocol_factory must be a callable returning a subclass of the asyncio.SubprocessProtocol 类。

其它参数：

• stdin can be any of these:

  • a file-like object representing a pipe to be connected to the subprocess’s standard input stream using connect_write_pipe()

  • subprocess.PIPE constant (default) which will create a new pipe and connect it,

  • 值 None which will make the subprocess inherit the file descriptor from this process

  • subprocess.DEVNULL constant which indicates that the special os.devnull file will be used

• stdout can be any of these:

  • a file-like object representing a pipe to be connected to the subprocess’s standard output stream using connect_write_pipe()

  • subprocess.PIPE constant (default) which will create a new pipe and connect it,

  • 值 None which will make the subprocess inherit the file descriptor from this process

  • subprocess.DEVNULL constant which indicates that the special os.devnull file will be used

• stderr can be any of these:

  • a file-like object representing a pipe to be connected to the subprocess’s standard error stream using connect_write_pipe()

  • subprocess.PIPE constant (default) which will create a new pipe and connect it,

  • 值 None which will make the subprocess inherit the file descriptor from this process

  • subprocess.DEVNULL constant which indicates that the special os.devnull file will be used

  • subprocess.STDOUT constant which will connect the standard error stream to the process’ standard output stream

• All other keyword arguments are passed to subprocess.Popen without interpretation, except for bufsize , universal_newlines , shell , text , encoding and errors , which should not be specified at all.

  asyncio subprocess API does not support decoding the streams as text. bytes.decode() can be used to convert the bytes returned from the stream to text.

See the constructor of the subprocess.Popen class for documentation on other arguments.

Returns a pair of (transport, protocol) ，其中 transport conforms to the asyncio.SubprocessTransport 基类和 protocol is an object instantiated by the protocol_factory .

coroutine loop. subprocess_shell ( protocol_factory , cmd , * , stdin=subprocess.PIPE , stdout=subprocess.PIPE , stderr=subprocess.PIPE , **kwargs ) ¶

创建子进程从 cmd , which can be a str 或 bytes string encoded to the 文件系统编码 , using the platform’s “shell” syntax.

This is similar to the standard library subprocess.Popen class called with shell=True .

protocol_factory must be a callable returning a subclass of the SubprocessProtocol 类。

见 subprocess_exec() for more details about the remaining arguments.

Returns a pair of (transport, protocol) ，其中 transport conforms to the SubprocessTransport 基类和 protocol is an object instantiated by the protocol_factory .

Hello World 采用 call_soon() ¶

范例使用 loop.call_soon() method to schedule a callback. The callback displays "Hello World" and then stops the event loop:

import asyncio
def hello_world(loop):
    """A callback to print 'Hello World' and stop the event loop"""
    print('Hello World')
    loop.stop()
loop = asyncio.get_event_loop()
# Schedule a call to hello_world()
loop.call_soon(hello_world, loop)
# Blocking call interrupted by loop.stop()
try:
    loop.run_forever()
finally:
    loop.close()
									

显示当前日期采用 call_later() ¶

An example of a callback displaying the current date every second. The callback uses the loop.call_later() method to reschedule itself after 5 seconds, and then stops the event loop:

import asyncio
import datetime
def display_date(end_time, loop):
    print(datetime.datetime.now())
    if (loop.time() + 1.0) < end_time:
        loop.call_later(1, display_date, end_time, loop)
    else:
        loop.stop()
loop = asyncio.get_event_loop()
# Schedule the first call to display_date()
end_time = loop.time() + 5.0
loop.call_soon(display_date, end_time, loop)
# Blocking call interrupted by loop.stop()
try:
    loop.run_forever()
finally:
    loop.close()
									

为读取事件看守文件描述符 ¶

Wait until a file descriptor received some data using the loop.add_reader() method and then close the event loop:

import asyncio
from socket import socketpair
# Create a pair of connected file descriptors
rsock, wsock = socketpair()
loop = asyncio.get_event_loop()
def reader():
    data = rsock.recv(100)
    print("Received:", data.decode())
    # We are done: unregister the file descriptor
    loop.remove_reader(rsock)
    # Stop the event loop
    loop.stop()
# Register the file descriptor for read event
loop.add_reader(rsock, reader)
# Simulate the reception of data from the network
loop.call_soon(wsock.send, 'abc'.encode())
try:
    # Run the event loop
    loop.run_forever()
finally:
    # We are done. Close sockets and the event loop.
    rsock.close()
    wsock.close()
    loop.close()
									

为 SIGINT 和 SIGTERM 设置信号处理程序 ¶

(This signals example only works on Unix.)

Register handlers for signals SIGINT and SIGTERM 使用 loop.add_signal_handler() 方法：

import asyncio
import functools
import os
import signal
def ask_exit(signame, loop):
    print("got signal %s: exit" % signame)
    loop.stop()
async def main():
    loop = asyncio.get_running_loop()
    for signame in {'SIGINT', 'SIGTERM'}:
        loop.add_signal_handler(
            getattr(signal, signame),
            functools.partial(ask_exit, signame, loop))
    await asyncio.sleep(3600)
print("Event loop running for 1 hour, press Ctrl+C to interrupt.")
print(f"pid {os.getpid()}: send SIGINT or SIGTERM to exit.")
asyncio.run(main())