asyncio-eventloop

asyncio
Event loop
Source code: 
Lib/asyncio/events.py, 
Lib/asyncio/base_events.py
Preface
The event loop is the core of every asyncio application. Event loops run asynchronous tasks and callbacks, perform network IO operations, and run subprocesses.
Application developers should typically use the high-level asyncio functions, such as 
asyncio.run, and should rarely need to reference the loop object or call its methods. This section is intended mostly for authors of lower-level code, libraries, and frameworks, who need finer control over the event loop behavior.
Obtaining the Event Loop
The following low-level functions can be used to get, set, or create an event loop:
get_running_loop()
Return the running event loop in the current OS thread.
Raise a 
RuntimeError if there is no running event loop.
This function can only be called from a coroutine or a callback.
3.7
get_event_loop()
Get the current event loop.
When called from a coroutine or a callback (e.g. scheduled with call_soon or similar API), this function will always return the running event loop.
If there is no running event loop set, the function will return the loop set by 
set_event_loop, or raise a 
RuntimeError if no loop has been set.
Because this function has rather complex behavior, using the 
get_running_loop function is preferred to 
get_event_loop in coroutines and callbacks.
As noted above, consider using the higher-level 
asyncio.run function, instead of using these lower level functions to manually create and close an event loop.
3.14 Raises a 
RuntimeError if there is no current event loop.
set_event_loop(loop)
Set loop as the current event loop for the current OS thread.
new_event_loop()
Create and return a new event loop object.
Contents
This documentation page contains the following sections:
The Event Loop Methods section is the reference documentation of the event loop APIs;
The Callback Handles section documents the 
Handle and 
TimerHandle instances which are returned from scheduling methods such as 
loop.call_soon and 
loop.call_later;
The Server Objects section documents types returned from event loop methods like 
loop.create_server;
The Event Loop Implementations section documents the 
SelectorEventLoop and 
ProactorEventLoop classes;
The Examples section showcases how to work with some event loop APIs.
Event loop methods
Event loops have low-level APIs for the following:
Running and stopping the loop
loop.run_until_complete(future)
Run until the future (an instance of 
Future) has completed.
If the argument is a 
coroutine object <coroutine> 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 is called.
If 
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.
If 
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 is called.
loop.stop()
Stop the event loop.
loop.is_running()
Return 
True if the event loop is currently running.
loop.is_closed()
Return 
True if the event loop was closed.
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.
loop.shutdown_asyncgens()
Schedule all currently open 
asynchronous generator objects to close with an 
~agen.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 is used.
Example:
try:
    loop.run_forever()
finally:
    loop.run_until_complete(loop.shutdown_asyncgens())
    loop.close()
3.6
loop.shutdown_default_executor(timeout=None)
Schedule the closure of the default executor and wait for it to join all of the threads in the 
~concurrent.futures.ThreadPoolExecutor. Once this method has been called, using the default executor with 
loop.run_in_executor will raise a 
RuntimeError.
The timeout parameter specifies the amount of time (in 
float seconds) the executor will be given to finish joining. With the default, 
None, the executor is allowed an unlimited amount of time.
If the timeout is reached, a 
RuntimeWarning is emitted and the default executor is terminated without waiting for its threads to finish joining.
[!NOTE]
Do not call this method when using 
asyncio.run, as the latter handles default executor shutdown automatically.
3.9
3.12 Added the timeout parameter.
Scheduling callbacks
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.
Return an instance of 
asyncio.Handle, which can be used later to cancel the callback.
Callbacks are called in the order in which they are registered. Each callback will be called exactly once.
The optional keyword-only context argument specifies a custom 
contextvars.Context for the callback to run in. Callbacks use the current context when no context is provided.
Unlike 
call_soon_threadsafe, this method is not thread-safe.
loop.call_soon_threadsafe(callback, *args, context=None)
A thread-safe variant of 
call_soon. When scheduling callbacks from another thread, this function must be used, since 
call_soon is not thread-safe.
This function is safe to be called from a reentrant context or signal handler, however, it is not safe or fruitful to use the returned handle in such contexts.
Raises 
RuntimeError if called on a loop that's been closed. This can happen on a secondary thread when the main application is shutting down.
See the 
concurrency and multithreading <asyncio-multithreading> section of the documentation.
3.7 The context keyword-only parameter was added. See 
567 for more details.
[!NOTE]
Most 
asyncio scheduling functions don't allow passing keyword arguments. To do that, use 
functools.partial:
# will schedule "print("Hello", flush=True)"
loop.call_soon(
    functools.partial(print, "Hello", flush=True))
Using partial objects is usually more convenient than using lambdas, as asyncio can render partial objects better in debug and error messages.
Scheduling delayed callbacks
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).
An instance of 
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. Use 
functools.partial 
to pass keyword arguments <asyncio-pass-keywords> to callback.
An optional keyword-only context argument allows specifying a custom 
contextvars.Context for the callback to run in. The current context is used when no context is provided.
[!NOTE]
For performance, callbacks scheduled with 
loop.call_later may run up to one clock-resolution early (see 
time.get_clock_info('monotonic').resolution).
3.7 The context keyword-only parameter was added. See 
567 for more details.
3.8 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.
An instance of 
asyncio.TimerHandle is returned which can be used to cancel the callback.
[!NOTE]
For performance, callbacks scheduled with 
loop.call_at may run up to one clock-resolution early (see 
time.get_clock_info('monotonic').resolution).
3.7 The context keyword-only parameter was added. See 
567 for more details.
3.8 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.
[!NOTE]
.. versionchanged:: 3.8 In Python 3.7 and earlier timeouts (relative delay or absolute when) should not exceed one day. This has been fixed in Python 3.8.
The 
asyncio.sleep function.
Creating futures and tasks
loop.create_future()
Create an 
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
loop.create_task(coro, , name=None, context=None, eager_start=None,*kwargs)
Schedule the execution of 
coroutine <coroutine> coro. Return a 
Task object.
Third-party event loops can use their own subclass of 
Task for interoperability. In this case, the result type is a subclass of 
Task.
The full function signature is largely the same as that of the 
Task constructor (or factory) - all of the keyword arguments to this function are passed through to that interface.
If the name argument is provided and not 
None, it is set as the name of the task using 
Task.set_name.
An optional keyword-only context argument allows specifying a custom 
contextvars.Context for the coro to run in. The current context copy is created when no context is provided.
An optional keyword-only eager_start argument allows specifying if the task should execute eagerly during the call to create_task, or be scheduled later. If eager_start is not passed the mode set by 
loop.set_task_factory will be used.
3.8 Added the name parameter.
3.11 Added the context parameter.
3.13.3 Added 
kwargs which passes on arbitrary extra parameters, including 
name and 
context.
3.13.4 Rolled back the change that passes on name and context (if it is None), while still passing on other arbitrary keyword arguments (to avoid breaking backwards compatibility with 3.13.3).
3.14 All kwargs are now passed on. The eager_start parameter works with eager task factories.
loop.set_task_factory(factory)
Set a task factory that will be used by 
loop.create_task.
If factory is 
None the default task factory will be set. Otherwise, factory must be a callable with the signature matching 
(loop, coro, **kwargs), where loop is a reference to the active event loop, and coro is a coroutine object. The callable must pass on all kwargs, and return a 
asyncio.Task-compatible object.
3.13.3 Required that all kwargs are passed on to 
asyncio.Task.
3.13.4 name is no longer passed to task factories. context is no longer passed to task factories if it is 
None.
3.14 name and context are now unconditionally passed on to task factories again.
loop.get_task_factory()
Return a task factory or 
None if the default one is in use.
Opening network connections
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, ssl_shutdown_timeout=None, happy_eyeballs_delay=None, interleave=None, all_errors=False)
Open a streaming transport connection to a given address specified by host and port.
The socket family can be either 
~socket.AF_INET or 
~socket.AF_INET6 depending on host (or the family argument, if provided).
The socket type will be 
~socket.SOCK_STREAM.
protocol_factory must be a callable returning an 
asyncio protocol <asyncio-protocol> implementation.
This method will try to establish the connection in the background. When successful, it returns a 
(transport, protocol) pair.
The chronological synopsis of the underlying operation is as follows:
The connection is established and a 
transport <asyncio-transport> is created for it.
protocol_factory is called without arguments and is expected to return a 
protocol <asyncio-protocol> instance.
The protocol instance is coupled with the transport by calling its 
~BaseProtocol.connection_made method.
A 
(transport, protocol) tuple is returned on success.
The created transport is an implementation-dependent bidirectional stream.
Other arguments:
ssl: if given and not false, a SSL/TLS transport is created (by default a plain TCP transport is created). If ssl is a 
ssl.SSLContext object, this context is used to create the transport; if ssl is 
True, a default context returned from 
ssl.create_default_context is used.
SSL/TLS security considerations <ssl-security>
server_hostname sets or overrides the hostname that the target server's certificate will be matched against. Should only be passed if ssl is not 
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. If server_hostname is an empty string, hostname matching is disabled (which is a serious security risk, allowing for potential man-in-the-middle attacks).
family, 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 
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 
8305. The default is 
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, family, proto, flags, happy_eyeballs_delay, interleave and local_addr should be specified.
[!NOTE]
The sock argument transfers ownership of the socket to the transport created. To close the socket, call the transport's 
~asyncio.BaseTransport.close method.
local_addr, if given, is a 
(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).
ssl_shutdown_timeout is the time in seconds to wait for the SSL shutdown to complete before aborting the connection. 
30.0 seconds if 
None (default).
all_errors determines what exceptions are raised when a connection cannot be created. By default, only a single 
Exception is raised: the first exception if there is only one or all errors have same message, or a single 
OSError with the error messages combined. When 
all_errors is 
True, an 
ExceptionGroup will be raised containing all exceptions (even if there is only one).
3.5
Added support for SSL/TLS in 
ProactorEventLoop.
3.6
The socket option 
socket.TCP_NODELAY <socket-unix-constants> is set by default for all TCP connections.
3.7
Added the ssl_handshake_timeout parameter.
3.8
Added the happy_eyeballs_delay and interleave parameters.
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.
For more information: https://datatracker.ietf.org/doc/html/rfc6555
3.11
Added the ssl_shutdown_timeout parameter.
3.12 all_errors was added.
3.16 Raises a 
ValueError if 
ssl.check_hostname is 
True and 
server_hostname is not supplied.
The 
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.
loop.create_datagram_endpoint(protocol_factory, local_addr=None, remote_addr=None, *, family=0, proto=0, flags=0, reuse_port=None, allow_broadcast=None, sock=None)
Create a datagram connection.
The socket family can be either 
~socket.AF_INET, 
~socket.AF_INET6, or 
~socket.AF_UNIX, depending on host (or the family argument, if provided).
The socket type will be 
~socket.SOCK_DGRAM.
protocol_factory must be a callable returning a 
protocol <asyncio-protocol> implementation.
A tuple of 
(transport, protocol) is returned on success.
Other arguments:
local_addr, if given, is a 
(local_host, local_port) tuple used to bind the socket locally. The local_host and local_port are looked up using 
getaddrinfo.
[!NOTE]
On Windows, when using the proactor event loop with 
local_addr=None, an 
OSError with 
!errno.WSAEINVAL will be raised when running it.
remote_addr, if given, is a 
(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.
family, 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 
socket.SO_REUSEPORT <socket-unix-constants> 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).
[!NOTE]
The sock argument transfers ownership of the socket to the transport created. To close the socket, call the transport's 
~asyncio.BaseTransport.close method.
See 
UDP echo client protocol <asyncio-udp-echo-client-protocol> and 
UDP echo server protocol <asyncio-udp-echo-server-protocol> examples.
3.4.4 The family, proto, flags, reuse_address, reuse_port, allow_broadcast, and sock parameters were added.
3.8 Added support for Windows.
3.8.1 The reuse_address parameter is no longer supported, as using 
socket.SO_REUSEADDR <socket-unix-constants> poses a significant security concern for UDP. Explicitly passing 
reuse_address=True will raise an exception.
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, 
socket.SO_REUSEPORT <socket-unix-constants> is used instead, which specifically prevents processes with differing UIDs from assigning sockets to the same socket address.
3.11 The reuse_address parameter, disabled since Python 3.8.1, 3.7.6 and 3.6.10, has been entirely removed.
loop.create_unix_connection(protocol_factory, path=None, *, ssl=None, sock=None, server_hostname=None, ssl_handshake_timeout=None, ssl_shutdown_timeout=None)
Create a Unix connection.
The socket family will be 
~socket.AF_UNIX; socket type will be 
~socket.SOCK_STREAM.
A tuple of 
(transport, protocol) is returned on success.
path is the name of a Unix domain socket and is required, unless a sock parameter is specified. Abstract Unix sockets, 
str, 
bytes, and 
~pathlib.Path paths are supported.
See the documentation of the 
loop.create_connection method for information about arguments to this method.
Unix.
3.7 Added the ssl_handshake_timeout parameter. The path parameter can now be a 
path-like object.
3.11
Added the ssl_shutdown_timeout parameter.
Creating network servers
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, keep_alive=None, ssl_handshake_timeout=None, ssl_shutdown_timeout=None, start_serving=True)
Create a TCP server (socket type 
~socket.SOCK_STREAM) listening on port of the host address.
Returns a 
Server object.
Arguments:
protocol_factory must be a callable returning a 
protocol <asyncio-protocol> implementation.
The host parameter can be set to several types which determine where the server would be listening:
If host is a string, the TCP server is bound to a single network interface specified by host.
If host is a sequence of strings, the TCP server is bound to all network interfaces specified by the sequence.
If 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).
The port parameter can be set to specify which port the server should listen on. If 
0 or 
None (the default), a random unused port will be selected (note that if host resolves to multiple network interfaces, a different random port will be selected for each interface).
family can be set to either 
socket.AF_INET or 
~socket.AF_INET6 to force the socket to use IPv4 or IPv6. If not set, the family will be determined from host name (defaults to 
~socket.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.
[!NOTE]
The sock argument transfers ownership of the socket to the server created. To close the socket, call the server's 
~asyncio.Server.close method.
backlog is the maximum number of queued connections passed to 
~socket.socket.listen (defaults to 100).
ssl can be set to an 
~ssl.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 on 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.
keep_alive set to 
True keeps connections active by enabling the periodic transmission of messages.
3.13
Added the keep_alive parameter.
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).
ssl_shutdown_timeout is the time in seconds to wait for the SSL shutdown to complete before aborting the connection. 
30.0 seconds if 
None (default).
start_serving set to 
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.
3.5
Added support for SSL/TLS in 
ProactorEventLoop.
3.5.1
The host parameter can be a sequence of strings.
3.6
Added ssl_handshake_timeout and start_serving parameters. The socket option 
socket.TCP_NODELAY <socket-unix-constants> is set by default for all TCP connections.
3.11
Added the ssl_shutdown_timeout parameter.
The 
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.
loop.create_unix_server(protocol_factory, path=None, *, sock=None, backlog=100, ssl=None, ssl_handshake_timeout=None, ssl_shutdown_timeout=None, start_serving=True, cleanup_socket=True, mode=None)
Similar to 
loop.create_server but works with the 
~socket.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, and 
~pathlib.Path paths are supported.
If cleanup_socket is true then the Unix socket will automatically be removed from the filesystem when the server is closed, unless the socket has been replaced after the server has been created.
If mode is not 
None, the permissions of the socket file created for path are changed to mode (as accepted by 
os.chmod) right after binding, before the server starts accepting connections, so a connection can never be accepted while the default, umask-derived permissions are still in effect. mode cannot be combined with sock and is not supported for abstract Unix sockets.
See the documentation of the 
loop.create_server method for information about arguments to this method.
Unix.
3.7
Added the ssl_handshake_timeout and start_serving parameters. The path parameter can now be a 
~pathlib.Path object.
3.11
Added the ssl_shutdown_timeout parameter.
3.13
Added the cleanup_socket parameter.
3.16
Added the mode parameter.
loop.connect_accepted_socket(protocol_factory, sock, *, ssl=None, ssl_handshake_timeout=None, ssl_shutdown_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.
Parameters:
protocol_factory must be a callable returning a 
protocol <asyncio-protocol> implementation.
sock is a preexisting socket object returned from 
socket.accept <socket.socket.accept>.
[!NOTE]
The sock argument transfers ownership of the socket to the transport created. To close the socket, call the transport's 
~asyncio.BaseTransport.close method.
ssl can be set to an 
~ssl.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).
ssl_shutdown_timeout is the time in seconds to wait for the SSL shutdown to complete before aborting the connection. 
30.0 seconds if 
None (default).
Returns a 
(transport, protocol) pair.
3.5.3
3.7
Added the ssl_handshake_timeout parameter.
3.11
Added the ssl_shutdown_timeout parameter.
Transferring files
loop.sendfile(transport, file, offset=0, count=None, *, fallback=True)
Send a 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() <io.IOBase.tell> can be used to obtain the actual number of bytes sent.
fallback set to 
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).
Raise 
SendfileNotAvailableError if the system does not support the sendfile syscall and fallback is 
False.
3.7
TLS upgrade
loop.start_tls(transport, protocol, sslcontext, *, server_side=False, server_hostname=None, ssl_handshake_timeout=None, ssl_shutdown_timeout=None)
Upgrade an existing transport-based connection to TLS.
Create a TLS coder/decoder instance and insert it between the transport and the protocol. The coder/decoder implements both transport-facing protocol and protocol-facing transport.
Return the created two-interface instance. After await, the protocol must stop using the original transport and communicate with the returned object only because the coder caches protocol-side data and sporadically exchanges extra TLS session packets with transport.
In some situations (e.g. when the passed transport is already closing) this may return 
None.
Parameters:
transport and protocol instances that methods like 
~loop.create_server and 
~loop.create_connection return.
sslcontext: a configured instance of 
~ssl.SSLContext.
server_side pass 
True when a server-side connection is being upgraded (like the one created by 
~loop.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).
ssl_shutdown_timeout is the time in seconds to wait for the SSL shutdown to complete before aborting the connection. 
30.0 seconds if 
None (default).
3.7
3.11
Added the ssl_shutdown_timeout parameter.
Watching file descriptors
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.
Any preexisting callback registered for fd is cancelled and replaced by callback.
loop.remove_reader(fd)
Stop monitoring the fd file descriptor for read availability. Returns 
True if fd was previously being monitored for reads.
loop.add_writer(fd, callback, *args)
Start monitoring the fd file descriptor for write availability and invoke callback with the specified arguments args once fd is available for writing.
Any preexisting callback registered for fd is cancelled and replaced by callback.
Use 
functools.partial 
to pass keyword arguments <asyncio-pass-keywords> to callback.
loop.remove_writer(fd)
Stop monitoring the fd file descriptor for write availability. Returns 
True if fd was previously being monitored for writes.
See also 
Platform Support <asyncio-platform-support> section for some limitations of these methods.
Working with socket objects directly
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.socket objects directly is more convenient.
loop.sock_recv(sock, nbytes)
Receive up to nbytes from sock. Asynchronous version of 
socket.recv() <socket.socket.recv>.
Return the received data as a bytes object.
sock must be a non-blocking socket.
3.7 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 method.
loop.sock_recv_into(sock, buf)
Receive data from sock into the buf buffer. Modeled after the blocking 
socket.recv_into() <socket.socket.recv_into> method.
Return the number of bytes written to the buffer.
sock must be a non-blocking socket.
3.7
loop.sock_recvfrom(sock, bufsize)
Receive a datagram of up to bufsize from sock. Asynchronous version of 
socket.recvfrom() <socket.socket.recvfrom>.
Return a tuple of (received data, remote address).
sock must be a non-blocking socket.
3.11
loop.sock_recvfrom_into(sock, buf, nbytes=0)
Receive a datagram of up to nbytes from sock into buf. Asynchronous version of 
socket.recvfrom_into() <socket.socket.recvfrom_into>.
Return a tuple of (number of bytes received, remote address).
sock must be a non-blocking socket.
3.11
loop.sock_sendall(sock, data)
Send data to the sock socket. Asynchronous version of 
socket.sendall() <socket.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 must be a non-blocking socket.
3.7 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 method.
loop.sock_sendto(sock, data, address)
Send a datagram from sock to address. Asynchronous version of 
socket.sendto() <socket.socket.sendto>.
Return the number of bytes sent.
sock must be a non-blocking socket.
3.11
loop.sock_connect(sock, address)
Connect sock to a remote socket at address.
Asynchronous version of 
socket.connect() <socket.socket.connect>.
sock must be a non-blocking socket.
With 
SelectorEventLoop, address does not need to be resolved: for 
~socket.AF_INET and 
~socket.AF_INET6 sockets, 
sock_connect first checks whether address is already resolved by calling 
socket.inet_pton, and uses 
loop.getaddrinfo to resolve it if it is not.
ProactorEventLoop, the default event loop on Windows, does not resolve address. The host must already be a numeric IP address; passing a host name raises 
OSError. Resolve the address with 
loop.getaddrinfo first, or use 
loop.create_connection, which resolves the address on every platform.
3.5.2 With 
SelectorEventLoop, 
address no longer needs to be resolved.
loop.create_connection and 
asyncio.open_connection() <open_connection>.
loop.sock_accept(sock)
Accept a connection. Modeled after the blocking 
socket.accept() <socket.socket.accept> method.
The socket must be bound to an address and listening for connections. The return value is a pair 
(conn, address) where conn is a new socket object usable to send and receive data on the connection, and address is the address bound to the socket on the other end of the connection.
sock must be a non-blocking socket.
3.7 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 method.
loop.create_server and 
start_server.
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() <socket.socket.sendfile>.
sock must be a non-blocking 
socket.SOCK_STREAM 
~socket.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() <io.IOBase.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).
Raise 
SendfileNotAvailableError if the system does not support sendfile syscall and fallback is 
False.
sock must be a non-blocking socket.
3.7
DNS
loop.getaddrinfo(host, port, *, family=0, type=0, proto=0, flags=0)
Asynchronous version of 
socket.getaddrinfo.
loop.getnameinfo(sockaddr, flags=0)
Asynchronous version of 
socket.getnameinfo.
[!NOTE]
Both getaddrinfo and getnameinfo internally utilize their synchronous versions through the loop's default thread pool executor. When this executor is saturated, these methods may experience delays, which higher-level networking libraries may report as increased timeouts. To mitigate this, consider using a custom executor for other user tasks, or setting a default executor with a larger number of workers.
3.7 Both getaddrinfo and getnameinfo methods were always documented to return a coroutine, but prior to Python 3.7 they were, in fact, returning 
asyncio.Future objects. Starting with Python 3.7 both methods are coroutines.
Working with pipes
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 <asyncio-protocol> implementation.
pipe is a 
file-like object <file object>. See 
Supported pipe objects <asyncio-pipe-objects> for the objects supported as pipe.
Return pair 
(transport, protocol), where transport supports the 
ReadTransport interface and protocol is an object instantiated by the protocol_factory.
With 
SelectorEventLoop event loop, the pipe is set to non-blocking mode.
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 <asyncio-protocol> implementation.
pipe is a 
file-like object <file object>. See 
Supported pipe objects <asyncio-pipe-objects> for the objects supported as pipe.
Return pair 
(transport, protocol), where 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.
Supported pipe objects
These methods only work with objects the operating system can poll for readiness or perform overlapped I/O on. Regular files on disk are not supported on any platform. There is no asynchronous file I/O in asyncio; use 
loop.run_in_executor to read and write regular files without blocking the event loop.
On Unix, with 
SelectorEventLoop, pipe must wrap one of the following:
a pipe, such as an end of an 
os.pipe pair or a FIFO created with 
os.mkfifo;
a socket;
a character device, such as a terminal.
On Windows, where only 
ProactorEventLoop implements these methods, pipe must wrap a handle opened for overlapped I/O (that is, created with the 
FILE_FLAG_OVERLAPPED flag), since the handle has to be associated with an I/O completion port. Handles that were not opened for overlapped I/O are rejected. In particular, the standard streams (
sys.stdin, 
sys.stdout and 
sys.stderr), console handles, and the pipes created by 
os.pipe are not opened for overlapped I/O and therefore cannot be used with these methods.
[!NOTE]
SelectorEventLoop does not support the above methods on Windows. Use 
ProactorEventLoop instead for Windows.
The 
loop.subprocess_exec and 
loop.subprocess_shell methods.
Unix signals
loop.add_signal_handler(signum, callback, *args)
Set callback as the handler for the signum signal, passing args as positional arguments.
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.
Raise 
ValueError if the signal number is invalid or uncatchable. Raise 
RuntimeError if there is a problem setting up the handler.
Use 
functools.partial 
to pass keyword arguments <asyncio-pass-keywords> to callback.
Like 
signal.signal, this function must be invoked in the main thread.
loop.remove_signal_handler(sig)
Remove the handler for the sig signal.
Return 
True if the signal handler was removed, or 
False if no handler was set for the given signal.
Unix.
The 
signal module.
Executing code in thread or process pools
loop.run_in_executor(executor, func, *args)
Arrange for func to be called in the specified executor passing args as positional arguments.
The executor argument should be an 
concurrent.futures.Executor instance. The default executor is used if executor is 
None. The default executor can be set by 
loop.set_default_executor, otherwise, a 
concurrent.futures.ThreadPoolExecutor will be lazy-initialized and used by 
run_in_executor if needed.
Example:
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)
    # 4. Run in a custom interpreter pool:
    with concurrent.futures.InterpreterPoolExecutor() as pool:
        result = await loop.run_in_executor(
            pool, cpu_bound)
        print('custom interpreter pool', result)
if __name__ == '__main__':
    asyncio.run(main())
Note that the entry point guard (
if __name__ == '__main__') is required for option 3 due to the peculiarities of 
multiprocessing, which is used by 
~concurrent.futures.ProcessPoolExecutor. See 
Safe importing of main module <multiprocessing-safe-main-import>.
This method returns a 
asyncio.Future object.
Use 
functools.partial 
to pass keyword arguments <asyncio-pass-keywords> to func.
3.5.3 
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 (
~concurrent.futures.ThreadPoolExecutor) to set the default.
loop.set_default_executor(executor)
Set executor as the default executor used by 
run_in_executor. executor must be an instance of 
~concurrent.futures.ThreadPoolExecutor, which includes 
~concurrent.futures.InterpreterPoolExecutor.
3.11 executor must be an instance of 
~concurrent.futures.ThreadPoolExecutor.
Error handling 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.
If handler is 
None, the default exception handler will be set. Otherwise, handler must be a callable with the signature matching 
(loop, context), where 
loop is a reference to the active event loop, and 
context is a 
dict object containing the details of the exception (see 
call_exception_handler documentation for details about context).
If the handler is called on behalf of a 
~asyncio.Task or 
~asyncio.Handle, it is run in the 
contextvars.Context of that task or callback handle.
3.12
The handler may be called in the 
~contextvars.Context of the task or handle where the exception originated.
loop.get_exception_handler()
Return the current exception handler, or 
None if no custom exception handler was set.
3.5.2
loop.default_exception_handler(context)
Default exception handler.
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 is a 
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 instance;
'task' (optional): 
asyncio.Task instance;
'handle' (optional): 
asyncio.Handle instance;
'protocol' (optional): 
Protocol <asyncio-protocol> instance;
'transport' (optional): 
Transport <asyncio-transport> instance;
'socket' (optional): 
socket.socket instance;
'source_traceback' (optional): Traceback of the source;
'handle_traceback' (optional): Traceback of the handle;
'asyncgen' (optional): Asynchronous generator that caused the exception.
[!NOTE]
This method should not be overloaded in subclassed event loops. For custom exception handling, use the 
set_exception_handler method.
Enabling debug mode
loop.get_debug()
Get the debug mode (
bool) of the event loop.
The default value is 
True if the environment variable 
PYTHONASYNCIODEBUG is set to a non-empty string, 
False otherwise.
loop.set_debug(enabled: bool)
Set the debug mode of the event loop.
3.7
The new 
Python Development Mode <devmode> can now also be used to enable the debug mode.
loop.slow_callback_duration
This attribute can be used to set the minimum execution duration in seconds that is considered "slow". When debug mode is enabled, "slow" callbacks are logged.
Default value is 100 milliseconds.
The 
debug mode of asyncio <asyncio-debug-mode>.
Running subprocesses
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.
[!NOTE]
On Windows, the default event loop 
ProactorEventLoop supports subprocesses, whereas 
SelectorEventLoop does not. See 
Subprocess Support on Windows <asyncio-windows-subprocess> for details.
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 
filesystem encoding <filesystem-encoding>.
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 
~subprocess.Popen takes a single argument which is list of strings, subprocess_exec takes multiple string arguments.
The protocol_factory must be a callable returning a subclass of the 
asyncio.SubprocessProtocol class.
Other parameters:
stdin can be any of these:
a file-like object
an existing file descriptor (a positive integer), for example those created with 
os.pipe
the 
subprocess.PIPE constant (default) which will create a new pipe and connect it,
the value 
None which will make the subprocess inherit the file descriptor from this process
the 
subprocess.DEVNULL constant which indicates that the special 
os.devnull file will be used
stdout can be any of these:
a file-like object
the 
subprocess.PIPE constant (default) which will create a new pipe and connect it,
the value 
None which will make the subprocess inherit the file descriptor from this process
the 
subprocess.DEVNULL constant which indicates that the special 
os.devnull file will be used
stderr can be any of these:
a file-like object
the 
subprocess.PIPE constant (default) which will create a new pipe and connect it,
the value 
None which will make the subprocess inherit the file descriptor from this process
the 
subprocess.DEVNULL constant which indicates that the special 
os.devnull file will be used
the 
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.
The 
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.
If a file-like object passed as stdin, stdout or stderr represents a pipe, then the other side of this pipe should be registered with 
~loop.connect_write_pipe or 
~loop.connect_read_pipe for use with the event loop.
See the constructor of the 
subprocess.Popen class for documentation on other arguments.
Returns a pair of 
(transport, protocol), where transport conforms to the 
asyncio.SubprocessTransport base class and protocol is an object instantiated by the protocol_factory.
If the transport is closed or is garbage collected, the child process is killed if it is still running.
loop.subprocess_shell(protocol_factory, cmd, , stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE,*kwargs)
Create a subprocess from cmd, which can be a 
str or a 
bytes string encoded to the 
filesystem encoding <filesystem-encoding>, using the platform's "shell" syntax.
This is similar to the standard library 
subprocess.Popen class called with 
shell=True.
The protocol_factory must be a callable returning a subclass of the 
SubprocessProtocol class.
See 
~loop.subprocess_exec for more details about the remaining arguments.
Returns a pair of 
(transport, protocol), where transport conforms to the 
SubprocessTransport base class and protocol is an object instantiated by the protocol_factory.
If the transport is closed or is garbage collected, the child process is killed if it is still running.
[!NOTE]
It is the application's responsibility to ensure that all whitespace and special characters are quoted appropriately to avoid shell injection vulnerabilities. The 
shlex.quote function can be used to properly escape whitespace and special characters in strings that are going to be used to construct shell commands.
Callback handles
A callback wrapper object returned by 
loop.call_soon, 
loop.call_soon_threadsafe.
get_context()
Return the 
contextvars.Context object associated with the handle.
3.12
cancel()
Cancel the callback. If the callback has already been canceled or executed, this method has no effect.
cancelled()
Return 
True if the callback was cancelled.
3.7
A callback wrapper object returned by 
loop.call_later, and 
loop.call_at.
This class is a subclass of 
Handle.
when()
Return a scheduled callback time as 
float seconds.
The time is an absolute timestamp, using the same time reference as 
loop.time.
3.7
Server objects
Server objects are created by 
loop.create_server, 
loop.create_unix_server, 
start_server, and 
start_unix_server functions.
Do not instantiate the 
Server class directly.
Server objects are asynchronous context managers. When used in an 
async with statement, it's guaranteed that the Server object is closed and not accepting new connections when the 
async with statement is completed:
srv = await loop.create_server(...)
async with srv:
    # some code
# At this point, srv is closed and no longer accepts new connections.
3.7 Server object is an asynchronous context manager since Python 3.7.
3.11 This class was exposed publicly as 
asyncio.Server in Python 3.9.11, 3.10.3 and 3.11.
close()
Stop serving: close listening sockets and set the 
sockets attribute to 
None.
The sockets that represent existing incoming client connections are left open.
The server is closed asynchronously; use the 
wait_closed coroutine to wait until the server is closed (and no more connections are active).
close_clients()
Close all existing incoming client connections.
Calls 
~asyncio.BaseTransport.close on all associated transports.
close should be called before 
close_clients when closing the server to avoid races with new clients connecting.
3.13
abort_clients()
Close all existing incoming client connections immediately, without waiting for pending operations to complete.
Calls 
~asyncio.WriteTransport.abort on all associated transports.
close should be called before 
abort_clients when closing the server to avoid races with new clients connecting.
3.13
get_loop()
Return the event loop associated with the server object.
3.7
start_serving()
Start accepting connections.
This method is idempotent, so it can be called when the server is already serving.
The start_serving keyword-only parameter to 
loop.create_server and 
asyncio.start_server allows creating a Server object that is not accepting connections initially. In this case 
Server.start_serving(), or 
Server.serve_forever can be used to make the Server start accepting connections.
3.7
serve_forever()
Start accepting connections until the coroutine is cancelled. Cancellation of 
serve_forever task causes the server to be closed.
This method can be called if the server is already accepting connections. Only one 
serve_forever task can exist per one Server object.
Example:
async def client_connected(reader, writer):
    # Communicate with the client with
    # reader/writer streams.  For example:
    await reader.readline()
async def main(host, port):
    srv = await asyncio.start_server(
        client_connected, host, port)
    await srv.serve_forever()
asyncio.run(main('127.0.0.1', 0))
3.7
is_serving()
Return 
True if the server is accepting new connections.
3.7
wait_closed()
Wait until the 
close method completes and all active connections have finished.
3.12 
wait_closed() now waits until the server is closed and all active connections have finished. Previously, it returned immediately if the server was already closed, even if connections were still active.
sockets
List of socket-like objects, 
asyncio.trsock.TransportSocket, which the server is listening on.
3.7 Prior to Python 3.7 
Server.sockets used to return an internal list of server sockets directly. In 3.7 a copy of that list is returned.
Event loop implementations
asyncio ships with two different event loop implementations: 
SelectorEventLoop and 
ProactorEventLoop.
By default asyncio is configured to use 
EventLoop.
A subclass of 
AbstractEventLoop based on the 
selectors module.
Uses the most efficient selector available for the given platform. It is also possible to manually configure the exact selector implementation to be used:
import asyncio
import selectors
async def main():
   ...
loop_factory = lambda: asyncio.SelectorEventLoop(selectors.SelectSelector())
asyncio.run(main(), loop_factory=loop_factory)
Unix, Windows.
A subclass of 
AbstractEventLoop for Windows that uses "I/O Completion Ports" (IOCP).
Windows.
MSDN documentation on I/O Completion Ports.
An alias to the most efficient available subclass of 
AbstractEventLoop for the given platform.
It is an alias to 
SelectorEventLoop on Unix and 
ProactorEventLoop on Windows.
3.13
Abstract base class for asyncio-compliant event loops.
The 
asyncio-event-loop-methods section lists all methods that an alternative implementation of 
AbstractEventLoop should have defined.
A base class that partially implements 
AbstractEventLoop to simplify writing custom event loops.
It provides default implementations of many 
AbstractEventLoop methods, so subclasses have fewer methods to implement themselves. In return, a subclass is expected to implement a number of internal, protected methods. See 
writing_custom_event_loop for more information.
Examples
Note that all examples in this section purposefully show how to use the low-level event loop APIs, such as 
loop.run_forever and 
loop.call_soon. Modern asyncio applications rarely need to be written this way; consider using the high-level functions like 
asyncio.run.
Hello World with call_soon()
An example using the 
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.new_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()
A similar 
Hello World <coroutine> example created with a coroutine and the 
run function.
Display the current date with 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 as dt
def display_date(end_time, loop):
    print(dt.datetime.now())
    if (loop.time() + 1.0) < end_time:
        loop.call_later(1, display_date, end_time, loop)
    else:
        loop.stop()
loop = asyncio.new_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()
A similar 
current date <asyncio_example_sleep> example created with a coroutine and the 
run function.
Watch a file descriptor for read events
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.new_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()
A similar 
example <asyncio_example_create_connection> using transports, protocols, and the 
loop.create_connection method.
Another similar 
example <asyncio_example_create_connection-streams> using the high-level 
asyncio.open_connection function and streams.
Set signal handlers for SIGINT and SIGTERM
(This 
signal example only works on Unix.)
Register handlers for signals 
~signal.SIGINT and 
~signal.SIGTERM using the 
loop.add_signal_handler method:
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())