Exceptions

+
Exceptions… allow error handling to be organized cleanly in a central or high-level place within the program structure.
+
— Doug Hellmann, Python Exception Handling Techniques
+

Exception handling in REST framework views

REST framework's views handle various exceptions, and deal with returning appropriate error responses.

The handled exceptions are:

Subclasses of APIException raised inside REST framework.
Django's Http404 exception.
Django's PermissionDenied exception.

In each case, REST framework will return a response with an appropriate status code and content-type. The body of the response will include any additional details regarding the nature of the error.

By default all error responses will include a key details in the body of the response, but other keys may also be included.

For example, the following request:

DELETE http://api.example.com/foo/bar HTTP/1.1
+Accept: application/json
+

Might receive an error response indicating that the DELETE method is not allowed on that resource:

HTTP/1.1 405 Method Not Allowed
+Content-Type: application/json
+Content-Length: 42
+
+{"detail": "Method 'DELETE' not allowed."}
+

Custom exception handling

You can implement custom exception handling by creating a handler function that converts exceptions raised in your API views into response objects. This allows you to control the style of error responses used by your API.

The function must take a single argument, which is the exception to be handled, and should either return a Response object, or return None if the exception cannot be handled. If the handler returns None then the exception will be re-raised and Django will return a standard HTTP 500 'server error' response.

For example, you might want to ensure that all error responses include the HTTP status code in the body of the response, like so:

HTTP/1.1 405 Method Not Allowed
+Content-Type: application/json
+Content-Length: 62
+
+{"status_code": 405, "detail": "Method 'DELETE' not allowed."}
+

In order to alter the style of the response, you could write the following custom exception handler:

from rest_framework.views import exception_handler
+
+def custom_exception_handler(exc):
+    # Call REST framework's default exception handler first,
+    # to get the standard error response.
+    response = exception_handler(exc)
+
+    # Now add the HTTP status code to the response.
+    if response is not None:
+        response.data['status_code'] = response.status_code
+
+    return response
+

The exception handler must also be configured in your settings, using the EXCEPTION_HANDLER setting key. For example:

REST_FRAMEWORK = {
+    'EXCEPTION_HANDLER': 'my_project.my_app.utils.custom_exception_handler'
+}
+

If not specified, the 'EXCEPTION_HANDLER' setting defaults to the standard exception handler provided by REST framework:

REST_FRAMEWORK = {
+    'EXCEPTION_HANDLER': 'rest_framework.views.exception_handler'
+}
+

Note that the exception handler will only be called for responses generated by raised exceptions. It will not be used for any responses returned directly by the view, such as the HTTP_400_BAD_REQUEST responses that are returned by the generic views when serializer validation fails.

API Reference

APIException

Signature: APIException()

The base class for all exceptions raised inside REST framework.

To provide a custom exception, subclass APIException and set the .status_code and .detail properties on the class.

ParseError

Signature: ParseError(detail=None)

Raised if the request contains malformed data when accessing request.DATA or request.FILES.

By default this exception results in a response with the HTTP status code "400 Bad Request".

AuthenticationFailed

Signature: AuthenticationFailed(detail=None)

Raised when an incoming request includes incorrect authentication.

By default this exception results in a response with the HTTP status code "401 Unauthenticated", but it may also result in a "403 Forbidden" response, depending on the authentication scheme in use. See the authentication documentation for more details.

NotAuthenticated

Signature: NotAuthenticated(detail=None)

Raised when an unauthenticated request fails the permission checks.

PermissionDenied

Signature: PermissionDenied(detail=None)

Raised when an authenticated request fails the permission checks.

By default this exception results in a response with the HTTP status code "403 Forbidden".

MethodNotAllowed

Signature: MethodNotAllowed(method, detail=None)

Raised when an incoming request occurs that does not map to a handler method on the view.

By default this exception results in a response with the HTTP status code "405 Method Not Allowed".

UnsupportedMediaType

Signature: UnsupportedMediaType(media_type, detail=None)

Raised if there are no parsers that can handle the content type of the request data when accessing request.DATA or request.FILES.

By default this exception results in a response with the HTTP status code "415 Unsupported Media Type".

Throttled

Signature: Throttled(wait=None, detail=None)

Raised when an incoming request fails the throttling checks.

By default this exception results in a response with the HTTP status code "429 Too Many Requests".