allow overriding synthesized properties

2 files changed, 38 insertions, 15 deletions

diff --git a/src/pyramid/util.py b/src/pyramid/util.py
index e552b37de..ca644dcce 100644
--- a/src/pyramid/util.py
+++ b/src/pyramid/util.py
@@ -73,6 +73,27 @@ def as_sorted_tuple(val):
     return val
 
 
+class SettableProperty(object):
+    def __init__(self, wrapped, name):
+        self.wrapped = wrapped
+        self.name = name
+        functools.update_wrapper(self, wrapped)
+
+    def __get__(self, obj, type=None):
+        if obj is None:  # pragma: no cover
+            return self
+        value = obj.__dict__.get(self.name, _marker)
+        if value is _marker:
+            value = self.wrapped(obj)
+        return value
+
+    def __set__(self, obj, value):
+        obj.__dict__[self.name] = value
+
+    def __delete__(self, obj):
+        del obj.__dict__[self.name]
+
+
 class InstancePropertyHelper(object):
     """A helper object for assigning properties and descriptors to instances.
     It is not normally possible to do this because descriptors must be
@@ -113,7 +134,7 @@ class InstancePropertyHelper(object):
 
             fn = pyramid.decorator.reify(fn)
         elif not is_property:
-            fn = property(fn)
+            fn = SettableProperty(fn, name)
 
         return name, fn
 
diff --git a/tests/test_util.py b/tests/test_util.py
index 293036c10..1553d8e60 100644
--- a/tests/test_util.py
+++ b/tests/test_util.py
@@ -103,25 +103,26 @@ class Test_InstancePropertyHelper(unittest.TestCase):
         )
 
     def test_override_property(self):
-        def worker(obj):  # pragma: no cover
+        def worker(obj):
             pass
 
         foo = Dummy()
         helper = self._getTargetClass()
         helper.set_property(foo, worker, name='x')
-
-        def doit():
-            foo.x = 1
-
-        self.assertRaises(AttributeError, doit)
+        self.assertIsNone(foo.x)
+        foo.x = 1
+        self.assertEqual(foo.x, 1)
+        del foo.x
+        self.assertIsNone(foo.x)
 
     def test_override_reify(self):
-        def worker(obj):  # pragma: no cover
+        def worker(obj):
             pass
 
         foo = Dummy()
         helper = self._getTargetClass()
         helper.set_property(foo, worker, name='x', reify=True)
+        self.assertIsNone(foo.x)
         foo.x = 1
         self.assertEqual(1, foo.x)
         foo.x = 2
@@ -301,23 +302,24 @@ class Test_InstancePropertyMixin(unittest.TestCase):
         )
 
     def test_override_property(self):
-        def worker(obj):  # pragma: no cover
+        def worker(obj):
             pass
 
         foo = self._makeOne()
         foo.set_property(worker, name='x')
-
-        def doit():
-            foo.x = 1
-
-        self.assertRaises(AttributeError, doit)
+        self.assertIsNone(foo.x)
+        foo.x = 1
+        self.assertEqual(foo.x, 1)
+        del foo.x
+        self.assertIsNone(foo.x)
 
     def test_override_reify(self):
-        def worker(obj):  # pragma: no cover
+        def worker(obj):
             pass
 
         foo = self._makeOne()
         foo.set_property(worker, name='x', reify=True)
+        self.assertIsNone(foo.x)
         foo.x = 1
         self.assertEqual(1, foo.x)
         foo.x = 2