Introduction to Perspective Broker

  1. Introduction
  2. Object Roadmap
  3. Things you can Call Remotely
  4. Things you can Copy Remotely


Suppose you find yourself in control of both ends of the wire: you have two programs that need to talk to each other, and you get to use any protocol you want. If you can think of your problem in terms of objects that need to make method calls on each other, then chances are good that you can use Twisted's Perspective Broker protocol rather than trying to shoehorn your needs into something like HTTP, or implementing yet another RPC mechanism1.

The Perspective Broker system (abbreviated PB, spawning numerous sandwich-related puns) is based upon a few central concepts:

This document will contain several examples that will (hopefully) appear redundant and verbose once you've figured out what's going on. To begin with, much of the code will just be labelled magic: don't worry about how these parts work yet. It will be explained more fully later.

Object Roadmap

To start with, here are the major classes, interfaces, and functions involved in PB, with links to the file where they are defined (all of which are under twisted/, of course). Don't worry about understanding what they all do yet: it's easier to figure them out through their interaction than explaining them one at a time.

Other classes that are involved at some point:

Classes and interfaces that get involved when you start to care about authorization and security:

Subclassing and Implementing

Technically you can subclass anything you want, but technically you could also write a whole new framework, which would just waste a lot of time. Knowing which classes are useful to subclass or which interfaces to implement is one of the bits of knowledge that's crucial to using PB (and all of Twisted) successfully. Here are some hints to get started:

Things you can Call Remotely

At this writing, there are three flavors of objects that can be accessed remotely through RemoteReference objects. Each of these flavors has a rule for how the callRemote message is transformed into a local method call on the server. In order to use one of these flavors, subclass them and name your published methods with the appropriate prefix.

Things you can Copy Remotely

In addition to returning objects that you can call remote methods on, you can return structured copies of local objects.

There are 2 basic flavors that allow for copying objects remotely. Again, you can use these by subclassing them. In order to specify what state you want to have copied when these are serialized, you can either use the Python default __getstate__ or specialized method calls for that flavor.


  1. Most of Twisted is like this. Hell, most of Unix is like this: if you think it would be useful, someone else has probably thought that way in the past, and acted on it, and you can take advantage of the tool they created to solve the same problem you're facing now.


Version: 12.3.0