Twisted (software)

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Twisted
Original author(s)Glyph Lefkowitz
Developer(s)Community
Initial releaseOctober 22, 2002; 21 years ago (2002-10-22)[1]
Stable release
24.7.0[2] Edit this on Wikidata / 10 August 2024; 2 months ago (10 August 2024)
Repository
Written inPython
TypeEvent-driven networking
LicenseMIT License
Websitewww.twistedmatrix.com Edit this on Wikidata

Twisted is an event-driven network programming framework written in Python and licensed under the MIT License.

Twisted projects variously support

callbacks
which are called by the framework.

Core ideas

Separation of protocols and transports

Twisted is designed for complete separation between logical protocols (usually relying on stream-based connection semantics, such as HTTP or

POP3) and physical transport layers supporting such stream-based semantics (such as files, sockets or SSL libraries). Connection between a logical protocol and a transport layer happens at the last possible moment — just before information is passed into the logical protocol instance. The logical protocol is informed of the transport layer instance, and can use it to send messages back and to check for the peer's identity. Note that it is still possible, in protocol code, to deeply query the transport layer on transport issues (such as checking a client-side SSL certificate). Naturally, such protocol code will fail (raise an exception
) if the transport layer does not support such semantics.

Deferreds

Central to the Twisted application model is the concept of a deferred (elsewhere called a

future
). A deferred is an instance of a class designed to receive and process a result which has not been computed yet, for example because it is based on data from a remote peer. Deferreds can be passed around, just like regular objects, but cannot be asked for their value. Each deferred supports a callback chain. When the deferred gets the value, it is passed to the functions on the callback chain, with the result of each callback becoming the input for the next. Deferreds make it possible to operate on the result of a function call before its value has become available.

For example, if a deferred returns a string from a remote peer containing an IP address in quad format, a callback can be attached to translate it into a 32-bit number. Any user of the deferred can now treat it as a deferred returning a 32-bit number. This, and the related ability to define "errbacks" (callbacks which are called as error handlers), allows code to specify in advance what to do when an asynchronous event occurs, without stopping to wait for the event. In non-event-driven systems, for example using threads, the operating system incurs premature and additional overhead organizing threads each time a blocking call is made.

Thread support

Twisted supports an abstraction over raw threads — using a thread as a deferred source. Thus, a deferred is returned immediately, which will receive a value when the thread finishes. Callbacks can be attached which will run in the main thread, thus alleviating the need for complex locking solutions. A prime example of such usage, which comes from Twisted's support libraries, is using this model to call into databases. The database call itself happens on a foreign thread, but the analysis of the result happens in the main thread.

Foreign loop support

Twisted can integrate with foreign event loops, such as those of

Qt and Cocoa (through PyObjC). This allows using Twisted as the network layer in graphical user interface
(GUI) programs, using all of its libraries without adding a thread-per-socket overhead, as using Python's native library would. A full-fledged web server can be integrated in-process with a GUI program using this model, for example.

Applications using Twisted

See also

References

  1. ^ Shtull-Trauring, Itamar (2002-10-22). "Twisted 1.0". twisted-python (Mailing list). Retrieved 2008-08-14.
  2. ^ "Release 24.7.0". 10 August 2024. Retrieved 27 August 2024.
  3. ^ "BuildBot Manual". github.com. Archived from the original on 2012-07-29. Retrieved 2017-10-28.
  4. ^ "Python Slithers into Systems". eweek.com.
  5. ^ SageMath#Features
  6. ^ Sage a Basic Overview[permanent dead link]
  7. ^ "mistah deejay". omegler.blogspot.com.
  8. ^ "Google Groups". groups.google.com.
  9. ^ "Calendar and Contacts Server". www.calendarserver.org.
  10. ^ "Twitch - Jobs". Twitch.
  11. ^ "Velocity Weather -". www.velocityweather.com.
  12. ^ A WebSocket-oriented monitor for Wikipedia (also, wikimon, wikital monsters), hatnote, 2017-09-03, retrieved 2017-09-21
  13. ^ "Deluge: build from source". dev.deluge-torrent.org. Retrieved 2020-01-08.
  14. ^ "Magic Wormhole". github.com.
  15. ^ "EventMachine". Retrieved 20 August 2011.
  16. ^ "Integrating with other Frameworks — Kivy 1.11.0.dev0 documentation". kivy.org.
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