HTTP Exceptions — Werkzeug Documentation (3.1.x)

# HTTP Exceptions

Implements a number of Python exceptions which can be raised from within a view to trigger a standard HTTP non-200 response.

## Usage Example

    from werkzeug.wrappers.request import Request
    from werkzeug.exceptions import HTTPException, NotFound

    def view(request):
        raise NotFound()

    @Request.application
    def application(request):
        try:
            return view(request)
        except HTTPException as e:
            return e

As you can see from this example those exceptions are callable WSGI applications. However, they are not Werkzeug response objects. You can get a response object by calling `get_response()` on a HTTP exception.

Keep in mind that you may have to pass an environ (WSGI) or scope (ASGI) to `get_response()` because some errors fetch additional information relating to the request.

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

    @Request.application
    def application(request):
        try:
            return view(request)
        except NotFound as e:
            return not_found(request)
        except HTTPException as e:
            return e

## Error Classes

The following error classes exist in Werkzeug:

exception werkzeug.exceptions.BadRequest(description=None, response=None)

  400 `Bad Request`

  Raise if the browser sends something to the application the application or server cannot handle.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.Unauthorized(description=None, response=None, www_authenticate=None)

  401 `Unauthorized`

  Raise if the user is not authorized to access a resource.

  The `www_authenticate` argument should be used to set the `WWW-Authenticate` header. This is used for HTTP basic auth and other schemes. Use `WWWAuthenticate` to create correctly formatted values. Strictly speaking a 401 response is invalid if it doesn’t provide at least one value for this header, although real clients typically don’t care.

  Parameters:

    - description (str | None) – Override the default message used for the body of the response.

    - www-authenticate – A single value, or list of values, for the WWW-Authenticate header(s).

    - response (SansIOResponse | None)

    - www_authenticate (None | (WWWAuthenticate | t.Iterable[WWWAuthenticate]))

  Return type:

    None

  Changelog

  Changed in version 2.0: Serialize multiple `www_authenticate` items into multiple `WWW-Authenticate` headers, rather than joining them into a single value, for better interoperability.

  Changed in version 0.15.3: If the `www_authenticate` argument is not set, the `WWW-Authenticate` header is not set.

  Changed in version 0.15.3: The `response` argument was restored.

  Changed in version 0.15.1: `description` was moved back as the first argument, restoring its previous position.

  Changed in version 0.15.0: `www_authenticate` was added as the first argument, ahead of `description`.

exception werkzeug.exceptions.Forbidden(description=None, response=None)

  403 `Forbidden`

  Raise if the user doesn’t have the permission for the requested resource but was authenticated.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.NotFound(description=None, response=None)

  404 `Not Found`

  Raise if a resource does not exist and never existed.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.MethodNotAllowed(valid_methods=None, description=None, response=None)

  405 `Method Not Allowed`

  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.

  The first argument for this exception should be a list of allowed methods. Strictly speaking the response would be invalid if you don’t provide valid methods in the header which you can do with that list.

  Takes an optional list of valid http methods starting with werkzeug 0.3 the list will be mandatory.

  Parameters:

    - valid_methods (t.Iterable[str] | None)

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.NotAcceptable(description=None, response=None)

  406 `Not Acceptable`

  Raise if the server can’t return any content conforming to the `Accept` headers of the client.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.RequestTimeout(description=None, response=None)

  408 `Request Timeout`

  Raise to signalize a timeout.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.Conflict(description=None, response=None)

  409 `Conflict`

  Raise to signal that a request cannot be completed because it conflicts with the current state on the server.

  Changelog

  Added in version 0.7.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.Gone(description=None, response=None)

  410 `Gone`

  Raise if a resource existed previously and went away without new location.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.LengthRequired(description=None, response=None)

  411 `Length Required`

  Raise if the browser submitted data but no `Content-Length` header which is required for the kind of processing the server does.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.PreconditionFailed(description=None, response=None)

  412 `Precondition Failed`

  Status code used in combination with `If-Match`, `If-None-Match`, or `If-Unmodified-Since`.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.RequestEntityTooLarge(description=None, response=None)

  413 `Request Entity Too Large`

  The status code one should return if the data submitted exceeded a given limit.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.RequestURITooLarge(description=None, response=None)

  414 `Request URI Too Large`

  Like 413 but for too long URLs.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.UnsupportedMediaType(description=None, response=None)

  415 `Unsupported Media Type`

  The status code returned if the server is unable to handle the media type the client transmitted.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.RequestedRangeNotSatisfiable(length=None, units='bytes', description=None, response=None)

  416 `Requested Range Not Satisfiable`

  The client asked for an invalid part of the file.

  Changelog

  Added in version 0.7.

  Takes an optional `Content-Range` header value based on `length` parameter.

  Parameters:

    - length (int | None)

    - units (str)

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.ExpectationFailed(description=None, response=None)

  417 `Expectation Failed`

  The server cannot meet the requirements of the Expect request-header.

  Changelog

  Added in version 0.7.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.ImATeapot(description=None, response=None)

  418 `I'm a teapot`

  The server should return this if it is a teapot and someone attempted to brew coffee with it.

  Changelog

  Added in version 0.7.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.MisdirectedRequest(description=None, response=None)

  421 Misdirected Request

  Indicates that the request was directed to a server that is not able to produce a response.

  Added in version 3.1.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.UnprocessableEntity(description=None, response=None)

  422 `Unprocessable Entity`

  Used if the request is well formed, but the instructions are otherwise incorrect.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.Locked(description=None, response=None)

  423 `Locked`

  Used if the resource that is being accessed is locked.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.FailedDependency(description=None, response=None)

  424 `Failed Dependency`

  Used if the method could not be performed on the resource because the requested action depended on another action and that action failed.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.PreconditionRequired(description=None, response=None)

  428 `Precondition Required`

  The server requires this request to be conditional, typically to prevent the lost update problem, which is a race condition between two or more clients attempting to update a resource through PUT or DELETE. By requiring each client to include a conditional header (“If-Match” or “If-Unmodified- Since”) with the proper value retained from a recent GET request, the server ensures that each client has at least seen the previous revision of the resource.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.TooManyRequests(description=None, response=None, retry_after=None)

  429 `Too Many Requests`

  The server is limiting the rate at which this user receives responses, and this request exceeds that rate. (The server may use any convenient method to identify users and their request rates). The server may include a “Retry-After” header to indicate how long the user should wait before retrying.

  Parameters:

    - retry_after (datetime | int | None) – If given, set the `Retry-After` header to this value. May be an `int` number of seconds or a `datetime`.

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

  Changelog

  Changed in version 1.0: Added `retry_after` parameter.

exception werkzeug.exceptions.RequestHeaderFieldsTooLarge(description=None, response=None)

  431 `Request Header Fields Too Large`

  The server refuses to process the request because the header fields are too large. One or more individual fields may be too large, or the set of all headers is too large.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.UnavailableForLegalReasons(description=None, response=None)

  451 `Unavailable For Legal Reasons`

  This status code indicates that the server is denying access to the resource as a consequence of a legal demand.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.InternalServerError(description=None, response=None, original_exception=None)

  500 `Internal Server Error`

  Raise if an internal server error occurred. This is a good fallback if an unknown error occurred in the dispatcher.

  Changelog

  Changed in version 1.0.0: Added the `original_exception` attribute.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

    - original_exception (BaseException | None)

  Return type:

    None

  original_exception

    The original exception that caused this 500 error. Can be used by frameworks to provide context when handling unexpected errors.

exception werkzeug.exceptions.NotImplemented(description=None, response=None)

  501 `Not Implemented`

  Raise if the application does not support the action requested by the browser.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.BadGateway(description=None, response=None)

  502 `Bad Gateway`

  If you do proxying 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.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.ServiceUnavailable(description=None, response=None, retry_after=None)

  503 `Service Unavailable`

  Status code you should return if a service is temporarily unavailable.

  Parameters:

    - retry_after (datetime | int | None) – If given, set the `Retry-After` header to this value. May be an `int` number of seconds or a `datetime`.

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

  Changelog

  Changed in version 1.0: Added `retry_after` parameter.

exception werkzeug.exceptions.GatewayTimeout(description=None, response=None)

  504 `Gateway Timeout`

  Status code you should return if a connection to an upstream server times out.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.HTTPVersionNotSupported(description=None, response=None)

  505 `HTTP Version Not Supported`

  The server does not support the HTTP protocol version used in the request.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.ClientDisconnected(description=None, response=None)

  Internal exception that is raised if Werkzeug detects a disconnected client. Since the client is already gone at that point attempting to send the error message to the client might not work and might ultimately result in another exception in the server. Mainly this is here so that it is silenced by default as far as Werkzeug is concerned.

  Since disconnections cannot be reliably detected and are unspecified by WSGI to a large extent this might or might not be raised if a client is gone.

  Changelog

  Added in version 0.8.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

exception werkzeug.exceptions.SecurityError(description=None, response=None)

  Raised if something triggers a security error. This is otherwise exactly like a bad request error.

  Changelog

  Added in version 0.9.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

## Baseclass

All the exceptions implement this common interface:

exception werkzeug.exceptions.HTTPException(description=None, response=None)

  The base class for all HTTP exceptions. This exception can be called as a WSGI application to render a default error page or you can catch the subclasses of it independently and render nicer error messages.

  Changelog

  Changed in version 2.1: Removed the `wrap` class method.

  Parameters:

    - description (str | None)

    - response (SansIOResponse | None)

  Return type:

    None

  get_response(environ: WSGIEnvironment | WSGIRequest | None = None, scope: None = None) → WSGIResponse
  get_response(environ: None = None, scope: dict[str, Any] = None) → SansIOResponse

    Get a response object.

    Parameters:

      - environ (WSGIEnvironment | WSGIRequest | None) – A WSGI environ dict or request object. If given, may be used to customize the response based on the request.

      - scope (dict[str, t.Any] | None) – An ASGI scope dict. If given, may be used to customize the response based on the request.

    Returns:

      A WSGI `werkzeug.wrappers.Response` if called without arguments or with `environ`. A sans-IO `werkzeug.sansio.Response` for ASGI if called with `scope`.

    Return type:

      WSGIResponse | SansIOResponse

  __call__(environ, start_response)

    Call the exception as WSGI application.

    Parameters:

      - environ (WSGIEnvironment) – the WSGI environment.

      - start_response (StartResponse) – the response callable provided by the WSGI server.

    Return type:

      t.Iterable[bytes]

## Special HTTP Exceptions

Starting with Werkzeug 0.3 some of the builtin classes raise exceptions that look like regular python exceptions (eg `KeyError`) but are `BadRequest` HTTP exceptions at the same time. This decision was made to simplify a common pattern where you want to abort if the client tampered with the submitted form data in a way that the application can’t recover properly and should abort with `400 BAD REQUEST`.

Assuming the application catches all HTTP exceptions and reacts to them properly a view function could do the following safely and doesn’t have to check if the keys exist:

    def new_post(request):
        post = Post(title=request.form['title'], body=request.form['body'])
        post.save()
        return redirect(post.url)

If `title` or `body` are missing in the form, a special key error will be raised which behaves like a `KeyError` but also a `BadRequest` exception.

exception werkzeug.exceptions.BadRequestKeyError(arg=None, *args, **kwargs)

  An exception that is used to signal both a `KeyError` and a `BadRequest`. Used by many of the datastructures.

  Parameters:

    - arg (object | None)

    - args (t.Any)

    - kwargs (t.Any)

## Simple Aborting

Sometimes it’s convenient to just raise an exception by the error code, without importing the exception and looking up the name etc. For this purpose there is the `abort()` function.

werkzeug.exceptions.abort(status, *args, **kwargs)

  Raises an `HTTPException` for the given status code or WSGI application.

  If a status code is given, it will be looked up in the list of exceptions and will raise that exception. If passed a WSGI application, it will wrap it in a proxy WSGI exception and raise that:

      abort(404)  # 404 Not Found
      abort(Response('Hello World'))

  Parameters:

    - status (int | SansIOResponse)

    - args (t.Any)

    - kwargs (t.Any)

  Return type:

    t.NoReturn

If you want to use this functionality with custom exceptions you can create an instance of the aborter class:

class werkzeug.exceptions.Aborter(mapping=None, extra=None)

  When passed a dict of code -> exception items it can be used as callable that raises exceptions. If the first argument to the callable is an integer it will be looked up in the mapping, if it’s a WSGI application it will be raised in a proxy exception.

  The rest of the arguments are forwarded to the exception constructor.

  Parameters:

    - mapping (dict[int, type[HTTPException]] | None)

    - extra (dict[int, type[HTTPException]] | None)

## Custom Errors

As you can see from the list above not all status codes are available as errors. Especially redirects and other non 200 status codes that 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 PaymentRequired(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.

You can override the default description in the constructor with the `description` parameter:

    raise BadRequest(description='Request failed because X was not present')