Low-level API Index — Python 3.8.2 documentation

# Low-level API Index

This page lists all low-level asyncio APIs.

## Obtaining the Event Loop

`asyncio.get_running_loop()` | The preferred function to get the running event loop.
`asyncio.get_event_loop()` | Get an event loop instance (current or via the policy).
`asyncio.set_event_loop()` | Set the event loop as current via the current policy.
`asyncio.new_event_loop()` | Create a new event loop.

Examples

- Using asyncio.get_running_loop().

## Event Loop Methods

See also the main documentation section about the event loop methods.

Lifecycle

`loop.run_until_complete()` | Run a Future/Task/awaitable until complete.
`loop.run_forever()` | Run the event loop forever.
`loop.stop()` | Stop the event loop.
`loop.close()` | Close the event loop.
`loop.is_running()` | Return `True` if the event loop is running.
`loop.is_closed()` | Return `True` if the event loop is closed.
`await` `loop.shutdown_asyncgens()` | Close asynchronous generators.

Debugging

`loop.set_debug()` | Enable or disable the debug mode.
`loop.get_debug()` | Get the current debug mode.

Scheduling Callbacks

`loop.call_soon()` | Invoke a callback soon.
`loop.call_soon_threadsafe()` | A thread-safe variant of `loop.call_soon()`.
`loop.call_later()` | Invoke a callback after the given time.
`loop.call_at()` | Invoke a callback at the given time.

Thread/Process Pool

`await` `loop.run_in_executor()` | Run a CPU-bound or other blocking function in a `concurrent.futures` executor.
`loop.set_default_executor()` | Set the default executor for `loop.run_in_executor()`.

Tasks and Futures

`loop.create_future()` | Create a `Future` object.
`loop.create_task()` | Schedule coroutine as a `Task`.
`loop.set_task_factory()` | Set a factory used by `loop.create_task()` to create `Tasks`.
`loop.get_task_factory()` | Get the factory `loop.create_task()` uses to create `Tasks`.

DNS

`await` `loop.getaddrinfo()` | Asynchronous version of `socket.getaddrinfo()`.
`await` `loop.getnameinfo()` | Asynchronous version of `socket.getnameinfo()`.

Networking and IPC

`await` `loop.create_connection()` | Open a TCP connection.
`await` `loop.create_server()` | Create a TCP server.
`await` `loop.create_unix_connection()` | Open a Unix socket connection.
`await` `loop.create_unix_server()` | Create a Unix socket server.
`await` `loop.connect_accepted_socket()` | Wrap a `socket` into a `(transport, protocol)` pair.
`await` `loop.create_datagram_endpoint()` | Open a datagram (UDP) connection.
`await` `loop.sendfile()` | Send a file over a transport.
`await` `loop.start_tls()` | Upgrade an existing connection to TLS.
`await` `loop.connect_read_pipe()` | Wrap a read end of a pipe into a `(transport, protocol)` pair.
`await` `loop.connect_write_pipe()` | Wrap a write end of a pipe into a `(transport, protocol)` pair.

Sockets

`await` `loop.sock_recv()` | Receive data from the `socket`.
`await` `loop.sock_recv_into()` | Receive data from the `socket` into a buffer.
`await` `loop.sock_sendall()` | Send data to the `socket`.
`await` `loop.sock_connect()` | Connect the `socket`.
`await` `loop.sock_accept()` | Accept a `socket` connection.
`await` `loop.sock_sendfile()` | Send a file over the `socket`.
`loop.add_reader()` | Start watching a file descriptor for read availability.
`loop.remove_reader()` | Stop watching a file descriptor for read availability.
`loop.add_writer()` | Start watching a file descriptor for write availability.
`loop.remove_writer()` | Stop watching a file descriptor for write availability.

Unix Signals

`loop.add_signal_handler()` | Add a handler for a `signal`.
`loop.remove_signal_handler()` | Remove a handler for a `signal`.

Subprocesses

`loop.subprocess_exec()` | Spawn a subprocess.
`loop.subprocess_shell()` | Spawn a subprocess from a shell command.

Error Handling

`loop.call_exception_handler()` | Call the exception handler.
`loop.set_exception_handler()` | Set a new exception handler.
`loop.get_exception_handler()` | Get the current exception handler.
`loop.default_exception_handler()` | The default exception handler implementation.

Examples

- Using asyncio.get_event_loop() and loop.run_forever().

- Using loop.call_later().

- Using `loop.create_connection()` to implement an echo-client.

- Using `loop.create_connection()` to connect a socket.

- Using add_reader() to watch an FD for read events.

- Using loop.add_signal_handler().

- Using loop.subprocess_exec().

## Transports

All transports implement the following methods:

`transport.close()` | Close the transport.
`transport.is_closing()` | Return `True` if the transport is closing or is closed.
`transport.get_extra_info()` | Request for information about the transport.
`transport.set_protocol()` | Set a new protocol.
`transport.get_protocol()` | Return the current protocol.

Transports that can receive data (TCP and Unix connections, pipes, etc). Returned from methods like `loop.create_connection()`, `loop.create_unix_connection()`, `loop.connect_read_pipe()`, etc:

Read Transports

`transport.is_reading()` | Return `True` if the transport is receiving.
`transport.pause_reading()` | Pause receiving.
`transport.resume_reading()` | Resume receiving.

Transports that can Send data (TCP and Unix connections, pipes, etc). Returned from methods like `loop.create_connection()`, `loop.create_unix_connection()`, `loop.connect_write_pipe()`, etc:

Write Transports

`transport.write()` | Write data to the transport.
`transport.writelines()` | Write buffers to the transport.
`transport.can_write_eof()` | Return `True` if the transport supports sending EOF.
`transport.write_eof()` | Close and send EOF after flushing buffered data.
`transport.abort()` | Close the transport immediately.
`transport.get_write_buffer_size()` | Return high and low water marks for write flow control.
`transport.set_write_buffer_limits()` | Set new high and low water marks for write flow control.

Transports returned by `loop.create_datagram_endpoint()`:

Datagram Transports

`transport.sendto()` | Send data to the remote peer.
`transport.abort()` | Close the transport immediately.

Low-level transport abstraction over subprocesses. Returned by `loop.subprocess_exec()` and `loop.subprocess_shell()`:

Subprocess Transports

`transport.get_pid()` | Return the subprocess process id.
`transport.get_pipe_transport()` | Return the transport for the requested communication pipe (stdin, stdout, or stderr).
`transport.get_returncode()` | Return the subprocess return code.
`transport.kill()` | Kill the subprocess.
`transport.send_signal()` | Send a signal to the subprocess.
`transport.terminate()` | Stop the subprocess.
`transport.close()` | Kill the subprocess and close all pipes.

## Protocols

Protocol classes can implement the following callback methods:

`callback` `connection_made()` | Called when a connection is made.
`callback` `connection_lost()` | Called when the connection is lost or closed.
`callback` `pause_writing()` | Called when the transport’s buffer goes over the high water mark.
`callback` `resume_writing()` | Called when the transport’s buffer drains below the low water mark.

Streaming Protocols (TCP, Unix Sockets, Pipes)

`callback` `data_received()` | Called when some data is received.
`callback` `eof_received()` | Called when an EOF is received.

Buffered Streaming Protocols

`callback` `get_buffer()` | Called to allocate a new receive buffer.
`callback` `buffer_updated()` | Called when the buffer was updated with the received data.
`callback` `eof_received()` | Called when an EOF is received.

Datagram Protocols

`callback` `datagram_received()` | Called when a datagram is received.
`callback` `error_received()` | Called when a previous send or receive operation raises an `OSError`.

Subprocess Protocols

`callback` `pipe_data_received()` | Called when the child process writes data into its stdout or stderr pipe.
`callback` `pipe_connection_lost()` | Called when one of the pipes communicating with the child process is closed.
`callback` `process_exited()` | Called when the child process has exited.

## Event Loop Policies

Policies is a low-level mechanism to alter the behavior of functions like `asyncio.get_event_loop()`. See also the main policies section for more details.

Accessing Policies

`asyncio.get_event_loop_policy()` | Return the current process-wide policy.
`asyncio.set_event_loop_policy()` | Set a new process-wide policy.
`AbstractEventLoopPolicy` | Base class for policy objects.