From 53ca0c02b0c399f4cf17a6e0f8a8504e4dde4e91 Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Wed, 20 Mar 2013 23:10:24 -0700
Subject: [PATCH] Add PreconditionFailed exception

---
 rest_framework/exceptions.py | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/rest_framework/exceptions.py b/rest_framework/exceptions.py
index 0c96ecdd5..9ceb64fe1 100644
--- a/rest_framework/exceptions.py
+++ b/rest_framework/exceptions.py
@@ -88,6 +88,14 @@ class Throttled(APIException):
             self.detail = detail or self.default_detail
 
 
+class PreconditionFailed(APIException):
+    status_code = status.HTTP_412_PRECONDITION_FAILED
+    default_detail = 'Object has been updated since you retrieved it.'
+
+    def __init__(self, detail=None):
+        self.detail = detail or self.default_detail
+
+
 class ConfigurationError(Exception):
     """
     Indicates an internal server error.