The Twisted Reactor Explained

Twisted’s reactor is the object that controls the main event loop. It allows data to be processed asynchronously and it loosely follows the titular Reactor Design Pattern.

What are the benefits

The Twisted reactor has two main benefits.

  1. Asynchronous computing.
  2. It implements a select loop and not a busy loop. This means that while idle, the reactor will not consume CPU by constantly checking to see if there is something to do.


How do I instantiate the Twisted reactor?

You don’t ever need to instantiate it, instead just import it. The twisted reactor is a Singleton. This means there is only ever one instance. If an instance of it does not already exist, then it is created at the time that it is imported.

How do I start it?

You can start the Twisted reactor by calling:

Before this point it will still exist, but will not act.

Similarly, you can stop the reactor by calling:


Which will shut the reactor down. Once it is shut down, it will no longer be processing functions, so restarting it programmatically from inside will be impossible.

Is there more than one implementation of the Twisted reactor?

Yes, there are multiple implementations of the Twisted reactor that you can import depending on what you require it to do.

You can find the various implementations in twisted.internet. The filenames follows the format *reactor.

By default, importing reactor will import an EPollReactor for Linux-based operating systems, and either PollReactor or SelectReactor for other operating systems.