- A new internal exception class (*not* an API) named

  ``repoze.bfg.exceptions.PredicateMismatch`` now exists.  This
  exception is currently raised when no constituent view of a
  multiview can be called (due to no predicate match).  Previously, in
  this situation, a ``repoze.bfg.exceptions.NotFound`` was raised.  We
  provide backwards compatibility for code that expected a
  ``NotFound`` to be raised when no predicates match by causing
  ``repoze.bfg.exceptions.PredicateMismatch`` to inherit from
  ``NotFound``.  This will cause any exception view registered for
  ``NotFound`` to be called when a predicate mismatch occurs, as was
  the previous behavior.

  There is however, one perverse case that will expose a backwards
  incompatibility.  If 1) you had a view that was registered as a
  member of a multiview 2) this view explicitly raised a ``NotFound``
  exception *in order to* proceed to the next predicate check in the
  multiview, that code will now behave differently: rather than
  skipping to the next view match, a NotFound will be raised to the
  top-level exception handling machinery instead.  For code to be
  depending upon the behavior of a view raising ``NotFound`` to
  proceed to the next predicate match, would be tragic, but not
  impossible, given that ``NotFound`` is a public interface.
  ``repoze.bfg.exceptions.PredicateMismatch`` is not a public API and
  cannot be depended upon by application code, so you should not
  change your view code to raise ``PredicateMismatch``.  Instead, move
  the logic which raised the ``NotFound`` exception in the view out
  into a custom view predicate.

1 files changed, 5 insertions, 4 deletions

diff --git a/repoze/bfg/configuration.py b/repoze/bfg/configuration.py
index 4073719b4..e5e8bc8f6 100644
--- a/repoze/bfg/configuration.py
+++ b/repoze/bfg/configuration.py
@@ -49,6 +49,7 @@ from repoze.bfg.compat import md5
 from repoze.bfg.events import WSGIApplicationCreatedEvent
 from repoze.bfg.exceptions import Forbidden
 from repoze.bfg.exceptions import NotFound
+from repoze.bfg.exceptions import PredicateMismatch
 from repoze.bfg.exceptions import ConfigurationError
 from repoze.bfg.i18n import get_localizer
 from repoze.bfg.log import make_stream_logger
@@ -1894,7 +1895,7 @@ class MultiView(object):
                 return view
             if view.__predicated__(context, request):
                 return view
-        raise NotFound(self.name)
+        raise PredicateMismatch(self.name)
 
     def __permitted__(self, context, request):
         view = self.match(context, request)
@@ -1911,9 +1912,9 @@ class MultiView(object):
         for order, view, phash in self.get_views(request):
             try:
                 return view(context, request)
-            except NotFound:
+            except PredicateMismatch:
                 continue
-        raise NotFound(self.name)
+        raise PredicateMismatch(self.name)
 
 def decorate_view(wrapped_view, original_view):
     if wrapped_view is original_view:
@@ -2130,7 +2131,7 @@ def _predicate_wrap(view, predicates):
     def predicate_wrapper(context, request):
         if all((predicate(context, request) for predicate in predicates)):
             return view(context, request)
-        raise NotFound('predicate mismatch for view %s' % view)
+        raise PredicateMismatch('predicate mismatch for view %s' % view)
     def checker(context, request):
         return all((predicate(context, request) for predicate in
                     predicates))