18.5. asyncio — Asynchronous I/O, event loop, coroutines and tasks — Python 3.6.15 documentation (original) (raw)
New in version 3.4.
Source code: Lib/asyncio/
This module provides infrastructure for writing single-threaded concurrent code using coroutines, multiplexing I/O access over sockets and other resources, running network clients and servers, and other related primitives. Here is a more detailed list of the package contents:
- a pluggable event loop with various system-specific implementations;
- transport and protocol abstractions (similar to those in Twisted);
- concrete support for TCP, UDP, SSL, subprocess pipes, delayed calls, and others (some may be system-dependent);
- a Future class that mimics the one in the concurrent.futuresmodule, but adapted for use with the event loop;
- coroutines and tasks based on
yield from(PEP 380), to help write concurrent code in a sequential fashion; - cancellation support for Futures and coroutines;
- synchronization primitives for use between coroutines in a single thread, mimicking those in the threading module;
- an interface for passing work off to a threadpool, for times when you absolutely, positively have to use a library that makes blocking I/O calls.
Asynchronous programming is more complex than classical “sequential” programming: see the Develop with asyncio page which lists common traps and explains how to avoid them. Enable the debug mode during development to detect common issues.
Table of contents:
- 18.5.1. Base Event Loop
- 18.5.1.1. Run an event loop
- 18.5.1.2. Calls
- 18.5.1.3. Delayed calls
- 18.5.1.4. Futures
- 18.5.1.5. Tasks
- 18.5.1.6. Creating connections
- 18.5.1.7. Creating listening connections
- 18.5.1.8. Watch file descriptors
- 18.5.1.9. Low-level socket operations
- 18.5.1.10. Resolve host name
- 18.5.1.11. Connect pipes
- 18.5.1.12. UNIX signals
- 18.5.1.13. Executor
- 18.5.1.14. Error Handling API
- 18.5.1.15. Debug mode
- 18.5.1.16. Server
- 18.5.1.17. Handle
- 18.5.1.18. Event loop examples
* 18.5.1.18.1. Hello World with call_soon()
* 18.5.1.18.2. Display the current date with call_later()
* 18.5.1.18.3. Watch a file descriptor for read events
* 18.5.1.18.4. Set signal handlers for SIGINT and SIGTERM
- 18.5.2. Event loops
- 18.5.2.1. Event loop functions
- 18.5.2.2. Available event loops
- 18.5.2.3. Platform support
* 18.5.2.3.1. Windows
* 18.5.2.3.2. Mac OS X - 18.5.2.4. Event loop policies and the default policy
- 18.5.2.5. Event loop policy interface
- 18.5.2.6. Access to the global loop policy
- 18.5.2.7. Customizing the event loop policy
- 18.5.3. Tasks and coroutines
- 18.5.3.1. Coroutines
* 18.5.3.1.1. Example: Hello World coroutine
* 18.5.3.1.2. Example: Coroutine displaying the current date
* 18.5.3.1.3. Example: Chain coroutines - 18.5.3.2. InvalidStateError
- 18.5.3.3. TimeoutError
- 18.5.3.4. Future
* 18.5.3.4.1. Example: Future with run_until_complete()
* 18.5.3.4.2. Example: Future with run_forever() - 18.5.3.5. Task
* 18.5.3.5.1. Example: Parallel execution of tasks - 18.5.3.6. Task functions
- 18.5.3.1. Coroutines
- 18.5.4. Transports and protocols (callback based API)
- 18.5.4.1. Transports
* 18.5.4.1.1. BaseTransport
* 18.5.4.1.2. ReadTransport
* 18.5.4.1.3. WriteTransport
* 18.5.4.1.4. DatagramTransport
* 18.5.4.1.5. BaseSubprocessTransport - 18.5.4.2. Protocols
* 18.5.4.2.1. Protocol classes
* 18.5.4.2.2. Connection callbacks
* 18.5.4.2.3. Streaming protocols
* 18.5.4.2.4. Datagram protocols
* 18.5.4.2.5. Flow control callbacks
* 18.5.4.2.6. Coroutines and protocols - 18.5.4.3. Protocol examples
* 18.5.4.3.1. TCP echo client protocol
* 18.5.4.3.2. TCP echo server protocol
* 18.5.4.3.3. UDP echo client protocol
* 18.5.4.3.4. UDP echo server protocol
* 18.5.4.3.5. Register an open socket to wait for data using a protocol
- 18.5.4.1. Transports
- 18.5.5. Streams (coroutine based API)
- 18.5.5.1. Stream functions
- 18.5.5.2. StreamReader
- 18.5.5.3. StreamWriter
- 18.5.5.4. StreamReaderProtocol
- 18.5.5.5. IncompleteReadError
- 18.5.5.6. LimitOverrunError
- 18.5.5.7. Stream examples
* 18.5.5.7.1. TCP echo client using streams
* 18.5.5.7.2. TCP echo server using streams
* 18.5.5.7.3. Get HTTP headers
* 18.5.5.7.4. Register an open socket to wait for data using streams
- 18.5.6. Subprocess
- 18.5.6.1. Windows event loop
- 18.5.6.2. Create a subprocess: high-level API using Process
- 18.5.6.3. Create a subprocess: low-level API using subprocess.Popen
- 18.5.6.4. Constants
- 18.5.6.5. Process
- 18.5.6.6. Subprocess and threads
- 18.5.6.7. Subprocess examples
* 18.5.6.7.1. Subprocess using transport and protocol
* 18.5.6.7.2. Subprocess using streams
- 18.5.7. Synchronization primitives
- 18.5.8. Queues
- 18.5.9. Develop with asyncio
- 18.5.9.1. Debug mode of asyncio
- 18.5.9.2. Cancellation
- 18.5.9.3. Concurrency and multithreading
- 18.5.9.4. Handle blocking functions correctly
- 18.5.9.5. Logging
- 18.5.9.6. Detect coroutine objects never scheduled
- 18.5.9.7. Detect exceptions never consumed
- 18.5.9.8. Chain coroutines correctly
- 18.5.9.9. Pending task destroyed
- 18.5.9.10. Close transports and event loops
See also
The asyncio module was designed in PEP 3156. For a motivational primer on transports and protocols, see PEP 3153.