HTTP Exceptions



The werkzeug.exceptions module implements a number of Python exceptions you can raise from within your views to trigger a standard non 200 response.

Usage Example

from werkzeug import BaseRequest, responder
from werkzeug.exceptions import HTTPException, NotFound

def view(request):
    raise NotFound()

def application(environ, start_response):
    request = BaseRequest(environ)
        return view(request)
    except HTTPException, e:
        return e

As you can see from this example those exceptions are callable WSGI applications. Because of Python 2.3 / 2.4 compatibility those do not extend from the response objects but only from the python exception class.

As a matter of fact they are not werkzeug response objects. However you can get a response object by calling get_response() on a HTTP exception.

Keep in mind that you have to pass an environment to get_response() because some errors fetch additional information from the WSGI environment.

If you want to hook in a different exception page to say, an 404 status code, you can add a second except for a specific subclass of an error:

def application(environ, start_response):
    request = BaseRequest(environ)
        return view(request)
    except NotFound, e:
        return not_found(request)
    except HTTPException, e:
        return e

Error Classes

The following error classes exists in Werkzeug:

400 BadRequest
Raise if the browser send something to the application the application or server cannot handle.
401 Unauthorized
Raise if the user is not authorized. Also used if you want to use HTTP basic auth.
403 Forbidden
Raise if the user doesn't have the permission for the requested resource but was authenticated.
404 NotFound
Raise if a resource does not exist and never existed.
405 MethodNotAllowed
Raise if the server used a method the resource does not handle. For example POST if the resource is view only. Especially useful for REST.
408 RequestTimeout
Raise to signalize a timeout.
410 Gone
Raise if a resource existed previously and went away without new location.
411 LengthRequired
Raise if the browser submitted data but no Content-Length header which is required for the kind of processing the server does.
412 PreconditionFailed
Status code used in combination with If-Match, If-None-Match, or If-Unmodified-Since.
413 RequestEntityTooLarge
The status code one should return if the data submitted exceeded a given limit.
414 RequestURITooLarge
Like 413 but for too long URLs.
415 UnsupportedMediaType
The status code returned if the server is unable to handle the media type the client transmitted.
500 InternalServerError
Raise if an internal server error occoured. This is a good fallback if an unknown error occoured in the dispatcher.
501 NotImplemented
Raise if the application does not support the action requested by the browser.
502 BadGateway
If you do proxing in your application you should return this status code if you received an invalid response from the upstream server it accessed in attempting to fulfill the request.
503 ServiceUnavailable
Status code you should return if a service is temporarily unavailable.

Custom Errors

As you can see from the list above not all status codes are available as errors. Especially redirects and ather non 200 status codes that represent do not represent errors are missing. For redirects you can use the redirect function from the utilities.

If you want to add an error yourself you can subclass HTTPException:

from werkzeug.exceptions import HTTPException

class PaymentRequred(HTTPException):
    code = 402
    description = '<p>Payment required.</p>'

This is the minimal code you need for your own exception. If you want to add more logic to the errors you can override the get_description(), get_body(), get_headers() and get_response() methods. In any case you should have a look at the sourcecode of the exceptions module.