Use overridden settings exception handler

Instead of using the api_settings exception handler, we use the
overridden settings attribute to find the correct handler.

Closes #5054

rest_framework/views.py

@@ -290,7 +290,7 @@ class APIView(View):
         """
         Returns the exception handler that this view uses.
         """
-        return api_settings.EXCEPTION_HANDLER
+        return self.settings.EXCEPTION_HANDLER
 
     # API policy implementation methods
 

tests/test_views.py

@@ -8,7 +8,7 @@ from django.test import TestCase
 from rest_framework import status
 from rest_framework.decorators import api_view
 from rest_framework.response import Response
-from rest_framework.settings import api_settings
+from rest_framework.settings import APISettings, api_settings
 from rest_framework.test import APIRequestFactory
 from rest_framework.views import APIView
 
@@ -45,6 +45,19 @@ class ErrorView(APIView):
         raise Exception
 
 
+def custom_handler(exc, context):
+    if isinstance(exc, SyntaxError):
+        return Response({'error': 'SyntaxError'}, status=400)
+    return Response({'error': 'UnknownError'}, status=500)
+
+
+class OverridenSettingsView(APIView):
+    settings = APISettings({'EXCEPTION_HANDLER': custom_handler})
+
+    def get(self, request, *args, **kwargs):
+        raise SyntaxError('request is invalid syntax')
+
+
 @api_view(['GET'])
 def error_view(request):
     raise Exception
@@ -118,3 +131,14 @@ class TestCustomExceptionHandler(TestCase):
         expected = 'Error!'
         assert response.status_code == status.HTTP_400_BAD_REQUEST
         assert response.data == expected
+
+
+class TestCustomSettings(TestCase):
+    def setUp(self):
+        self.view = OverridenSettingsView.as_view()
+
+    def test_get_exception_handler(self):
+        request = factory.get('/', content_type='application/json')
+        response = self.view(request)
+        assert response.status_code == 400
+        assert response.data == {'error': 'SyntaxError'}