allow the execution policy to perform a last-ditch effort to render an exception view

2 files changed, 39 insertions, 2 deletions

diff --git a/pyramid/router.py b/pyramid/router.py
index 8b7b7b6bc..7f3f9fbea 100644
--- a/pyramid/router.py
+++ b/pyramid/router.py
@@ -1,3 +1,4 @@
+import sys
 from zope.interface import (
     implementer,
     providedBy,
@@ -24,6 +25,7 @@ from pyramid.events import (
     BeforeTraversal,
     )
 
+from pyramid.compat import reraise
 from pyramid.httpexceptions import HTTPNotFound
 from pyramid.request import Request
 from pyramid.view import _call_view
@@ -252,7 +254,15 @@ class Router(object):
         response = self.execution_policy(environ, self)
         return response(environ, start_response)
 
-
 def default_execution_policy(environ, router):
     request = router.make_request(environ)
-    return router.invoke_request(request)
+    try:
+        return router.invoke_request(request)
+    except Exception:
+        exc_info = sys.exc_info()
+        try:
+            return request.invoke_exception_view(exc_info)
+        except HTTPNotFound:
+            reraise(*exc_info)
+        finally:
+            del exc_info  # avoid local ref cycle
diff --git a/pyramid/tests/test_router.py b/pyramid/tests/test_router.py
index a5da5c627..bd023824c 100644
--- a/pyramid/tests/test_router.py
+++ b/pyramid/tests/test_router.py
@@ -1284,6 +1284,33 @@ class TestRouter(unittest.TestCase):
         self.assertEqual(resp.status_code, 200)
         self.assertEqual(resp.body, b'foo')
 
+    def test_execution_policy_handles_exception(self):
+        from pyramid.interfaces import IViewClassifier
+        from pyramid.interfaces import IExceptionViewClassifier
+        from pyramid.interfaces import IRequest
+        class Exception1(Exception):
+            pass
+        class Exception2(Exception):
+            pass
+        req_iface = self._registerRouteRequest('foo')
+        self._connectRoute('foo', 'archives/:action/:article', None)
+        view = DummyView(DummyResponse(), raise_exception=Exception1)
+        self._registerView(view, '', IViewClassifier, req_iface, None)
+        exception_view1 = DummyView(DummyResponse(),
+                                    raise_exception=Exception2)
+        self._registerView(exception_view1, '', IExceptionViewClassifier,
+                           IRequest, Exception1)
+        response = DummyResponse()
+        response.app_iter = ["Hello, world"]
+        exception_view2 = DummyView(response)
+        self._registerView(exception_view2, '', IExceptionViewClassifier,
+                           IRequest, Exception2)
+        environ = self._makeEnviron(PATH_INFO='/archives/action1/article1')
+        start_response = DummyStartResponse()
+        router = self._makeOne()
+        result = router(environ, start_response)
+        self.assertEqual(result, ["Hello, world"])
+
 class DummyPredicate(object):
     def __call__(self, info, request):
         return True