# The RequestHandler Class - Google App Engine - Google Code

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# The RequestHandler Class

The RequestHandler class is the superclass for an HTTP request handler.

`RequestHandler` is provided by the `google.appengine.ext.webapp` module.

- Introduction
- RequestHandler()
- Instance methods:
  - get()
  - post()
  - put()
  - head()
  - options()
  - delete()
  - trace()
  - handle_exception()
  - error()
  - redirect()
  - initialize()
- Instance attributes:
  - request
  - response

## Introduction

A webapp application defines one or more RequestHandler classes to handle requests. A handler class overrides one or more of the following methods to handle HTTP requests of the corresponding kind: get(), post(), head(), options(), put(), delete(), or trace().

## Constructor

class RequestHandler()

  The base class for an HTTP request handler.

  The constructor takes no arguments. The instance can be initialized with the initialize() method.

## Instance Methods

Subclasses of the RequestHandler class inherit or override the following methods:

get(*args)
  Called to handle an HTTP GET request. Overridden by handler subclasses.
post(*args)
  Called to handle an HTTP POST request. Overridden by handler subclasses.
put(*args)
  Called to handle an HTTP PUT request. Overridden by handler subclasses.
head(*args)
  Called to handle an HTTP HEAD request. Overridden by handler subclasses.
options(*args)
  Called to handle an HTTP OPTIONS request. Overridden by handler subclasses.
delete(*args)
  Called to handle an HTTP DELETE request. Overridden by handler subclasses.
trace(*args)
  Called to handle an HTTP TRACE request. Overridden by handler subclasses.
handle_exception(exception, debug_mode)
  Called when an exception is raised by a handler. By default, handle_exception sets an HTTP status code of 500 ("Server error"). If debug_mode is `True` it prints a stack trace to the browser. Otherwise it just prints a plain error message. A RequestHandler class can override this method to provide custom behavior.
error(code)
  A shortcut method for handlers to use to return an error response. Clears the response output stream and sets the HTTP error code to code. Equivalent to calling `self.response.clear()` and `self.response.set_status(code)`.
redirect(uri, permanent=False)
  A shortcut method for handlers to use to return a redirect response. Sets the HTTP error code and `Location:` header to redirect to uri, and clears the response output stream. If permanent is `True`, it uses the HTTP status code 301 for a permanent redirect. Otherwise, it uses the HTTP status code 302 for a temporary redirect.
initialize(request, response)
  Initializes the handler instance with Request and Response objects. Typically, the WSGIApplication does this after instantiating the handler class.

## Instance Attributes

An instance of a subclass of RequestHandler has the following attributes:

`request`
  A Request instance. Typically, this attribute is initialized by the WSGIApplication after the object is constructed.
`response`
  A Response instance. Typically, this attribute is initialized by the WSGIApplication after the object is constructed.