Merge pull request #836 from markshannon/python-mutating-descriptor

Python: Fix up mutating-descriptor query

python/ql/test/query-tests/Classes/descriptors/MutatingDescriptor.expected

@@ -1 +1,2 @@
 | test.py:10:9:10:19 | Attribute | Mutation of descriptor $@ object may lead to action-at-a-distance effects or race conditions for properties. | test.py:3:1:3:33 | class MutatingDescriptor | MutatingDescriptor |
+| test.py:25:9:25:19 | Attribute | Mutation of descriptor $@ object may lead to action-at-a-distance effects or race conditions for properties. | test.py:3:1:3:33 | class MutatingDescriptor | MutatingDescriptor |

python/ql/test/query-tests/Classes/descriptors/test.py

@@ -1,14 +1,25 @@
 
 #This is prone to strange side effects and race conditions.
 class MutatingDescriptor(object):
-    
+
     def __init__(self, func):
         self.my_func = func
-        
+
     def __get__(self, obj, obj_type):
-        #Modified state is visible to all instances of C that might call "show".
+        #Modified state is visible to all instances.
         self.my_obj = obj
         return self
-        
+
     def __call__(self, *args):
-        return self.my_func(self.my_obj, *args)
+        return self.my_func(self.my_obj, *args)
+
+    #Not call from __get__, __set__ or __delete__
+    def ok(self, func):
+        self.my_func = func
+
+    def __set__(self, obj, value):
+        self.not_ok(value)
+
+    def not_ok(self, value):
+        #Modified state is visible to all instances.
+        self.my_obj = value