refactor tween initialization to occur at config-time

previously the EXCVIEW tween was only created in the router OR when
another tween is added. Now the EXCVIEW tween is just added at startup
similar to how view derivers and many other things operate.

4 files changed, 8 insertions, 18 deletions

diff --git a/pyramid/config/__init__.py b/pyramid/config/__init__.py
index 958526386..d4064dc78 100644
--- a/pyramid/config/__init__.py
+++ b/pyramid/config/__init__.py
@@ -379,6 +379,7 @@ class Configurator(
         self.add_default_view_predicates()
         self.add_default_view_derivers()
         self.add_default_route_predicates()
+        self.add_default_tweens()
 
         if exceptionresponse_view is not None:
             exceptionresponse_view = self.maybe_dotted(exceptionresponse_view)
diff --git a/pyramid/config/tweens.py b/pyramid/config/tweens.py
index 8e1800f33..0aeb01fe3 100644
--- a/pyramid/config/tweens.py
+++ b/pyramid/config/tweens.py
@@ -10,7 +10,6 @@ from pyramid.compat import (
 from pyramid.exceptions import ConfigurationError
 
 from pyramid.tweens import (
-    excview_tween_factory,
     MAIN,
     INGRESS,
     EXCVIEW,
@@ -107,6 +106,9 @@ class TweensConfiguratorMixin(object):
         return self._add_tween(tween_factory, under=under, over=over,
                                explicit=False)
 
+    def add_default_tweens(self):
+        self.add_tween(EXCVIEW)
+
     @action_method
     def _add_tween(self, tween_factory, under=None, over=None, explicit=False):
 
@@ -142,17 +144,6 @@ class TweensConfiguratorMixin(object):
         if tweens is None:
             tweens = Tweens()
             registry.registerUtility(tweens, ITweens)
-            ex_intr = self.introspectable('tweens',
-                                          ('tween', EXCVIEW, False),
-                                          EXCVIEW,
-                                          'implicit tween')
-            ex_intr['name'] = EXCVIEW
-            ex_intr['factory'] = excview_tween_factory
-            ex_intr['type'] = 'implicit'
-            ex_intr['under'] = None
-            ex_intr['over'] = MAIN
-            introspectables.append(ex_intr)
-            tweens.add_implicit(EXCVIEW, excview_tween_factory, over=MAIN)
 
         def register():
             if explicit:
diff --git a/pyramid/router.py b/pyramid/router.py
index 19773cf62..fd11925e9 100644
--- a/pyramid/router.py
+++ b/pyramid/router.py
@@ -34,8 +34,6 @@ from pyramid.traversal import (
     ResourceTreeTraverser,
     )
 
-from pyramid.tweens import excview_tween_factory
-
 @implementer(IRouter)
 class Router(object):
 
@@ -51,11 +49,10 @@ class Router(object):
         self.routes_mapper = q(IRoutesMapper)
         self.request_factory = q(IRequestFactory, default=Request)
         self.request_extensions = q(IRequestExtensions)
-        tweens = q(ITweens)
-        if tweens is None:
-            tweens = excview_tween_factory
         self.orig_handle_request = self.handle_request
-        self.handle_request = tweens(self.handle_request, registry)
+        tweens = q(ITweens)
+        if tweens is not None:
+            self.handle_request = tweens(self.handle_request, registry)
         self.root_policy = self.root_factory # b/w compat
         self.registry = registry
         settings = registry.settings
diff --git a/pyramid/testing.py b/pyramid/testing.py
index ec06fe379..877b351db 100644
--- a/pyramid/testing.py
+++ b/pyramid/testing.py
@@ -478,6 +478,7 @@ def setUp(registry=None, request=None, hook_zca=True, autocommit=True,
         config.add_default_view_predicates()
         config.add_default_view_derivers()
         config.add_default_route_predicates()
+        config.add_default_tweens()
     config.commit()
     global have_zca
     try: