# Overview of Twisted Web

## Abstract

Twisted Web is a web application server written in pure Python, with APIs at multiple levels of abstraction to facilitate different kinds of web programming. The most useful for web application designers is Web Widgets, a high-level class-and-template oriented system. There is also the Resource system, which Web Widgets is built on.

## Twisted Web's Structure

When the Web Server receives a request from a Client, it creates a Request object and passes it on to the Resource system. The Resource system dispatches to the appropriate Resource object based on what path was requested by the client. The Resource is asked to render itself, and the result is returned to the client.

## Resources

Resources are the lowest-level abstraction for applications in the Twisted web server. Each Resource is a 1:1 mapping with a path that is requested: you can think of a Resource as a single "page" to be rendered. The interface for making Resources is very simple; they must have a method named `render` which takes a single argument, which is the Request object (an instance of `twisted.web.server.Request`). This render method must return a string, which will be returned to the web browser making the request. Alternatively, they can return a special constant, `twisted.web.server.NOT_DONE_YET`, which tells the web server not to close the connection; you must then use `request.write(data)` to render the page, and call `request.finish()` whenever you're done. There is more information about developing software with Resources in the Resources, CGIs, Static Content, and Linking document.

## Widgets

Web Widgets are an added layer of abstraction of Resources -- they're much nicer for most sorts of web applications. For more information on Widgets, see Introducing Web Widgets.

Last modified: Tue Mar 12 22:47:46 EST 2002