Merge pull request #3559 from mmerickel/settable-properties

allow overriding synthesized properties

3 files changed, 63 insertions, 31 deletions

diff --git a/CHANGES.rst b/CHANGES.rst
index 383906e00..70ee43b96 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -71,6 +71,13 @@ Features
 - Fix ``DeprecationWarning`` emitted by using the ``imp`` module.
   See https://github.com/Pylons/pyramid/pull/3553
 
+- Properties created via ``config.add_request_method(..., property=True)`` or
+  ``request.set_property`` used to be readonly. They can now be overridden
+  via ``request.foo = ...`` and until the value is deleted it will return
+  the overridden value. This is most useful when mocking request properties
+  in testing.
+  See https://github.com/Pylons/pyramid/pull/3559
+
 Deprecations
 ------------
 
diff --git a/src/pyramid/util.py b/src/pyramid/util.py
index e552b37de..504516631 100644
--- a/src/pyramid/util.py
+++ b/src/pyramid/util.py
@@ -73,6 +73,26 @@ def as_sorted_tuple(val):
     return val
 
 
+class SettableProperty(object):
+    def __init__(self, wrapped):
+        self.wrapped = wrapped
+        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.wrapped.__name__, _marker)
+        if value is _marker:
+            value = self.wrapped(obj)
+        return value
+
+    def __set__(self, obj, value):
+        obj.__dict__[self.wrapped.__name__] = value
+
+    def __delete__(self, obj):
+        del obj.__dict__[self.wrapped.__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
@@ -94,26 +114,29 @@ class InstancePropertyHelper(object):
         (name, property) pair.
         """
 
-        is_property = isinstance(callable, property)
-        if is_property:
-            fn = callable
-            if name is None:
-                raise ValueError('must specify "name" for a property')
-            if reify:
-                raise ValueError('cannot reify a property')
-        elif name is not None:
-            fn = lambda this: callable(this)
-            fn.__name__ = get_callable_name(name)
-            fn.__doc__ = callable.__doc__
-        else:
+        if name is None:
+            if not hasattr(callable, '__name__'):
+                raise ValueError(
+                    'missing __name__, must specify "name" for property'
+                )
             name = callable.__name__
+        name = get_callable_name(name)
+        is_data_descriptor = hasattr(callable, '__set__')
+        if reify and is_data_descriptor:
+            raise ValueError('cannot reify a data descriptor')
+        if is_data_descriptor:
             fn = callable
-        if reify:
-            import pyramid.decorator  # avoid circular import
+        else:
+            wrapped = lambda this: callable(this)
+            wrapped.__name__ = name
+            wrapped.__doc__ = callable.__doc__
+
+            if reify:
+                import pyramid.decorator  # avoid circular import
 
-            fn = pyramid.decorator.reify(fn)
-        elif not is_property:
-            fn = property(fn)
+                fn = pyramid.decorator.reify(wrapped)
+            else:
+                fn = SettableProperty(wrapped)
 
         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