1. Basics
  The reactor is the core of the event loop with Twisted - the loop which drives applications using Twisted. The reactor provides basic interfaces to a number of services, including network communications, threading, and event dispatching.

There are multiple implementations of the reactor, each modified to provide better support for specialized features over the default implementation.

Twisted applications can use the interfaces in twisted.application.service to configure and run the application instead of using boilerplate reactor code.

2. Using the reactor object
  You can get to the reactor object using the following code:
    from twisted.internet import reactor

  The reactor usually implements a set of interfaces, but depending on the chosen reactor and the platform, some of the interfaces may not be implemented:
  IReactorCore: Core(required) functionality.
  IReactorFDSet: Use FileDescriptor objects.
  IReactorProcess: Process management.
  IReactorSSL: SSL networking support.
  IReactorTCP: TCP networking support.
  IReactorThreads: Threading use and management.
  IReactorTime: Scheduling interface.
  IReactorUDP: UDP networking support.
  IReactorUNIX: UNIX socket support.