Merge 97730a0 into ee24692

param/parameterized.py

@@ -512,8 +512,10 @@ def __setattr__(self,attribute,value):
         super(Parameter, self).__setattr__(attribute, value)
 
         if old is not NotImplemented:
+            change = Change(what=attribute,name=self._attrib_name,obj=None,cls=self._owner,old=old,new=value)
             for subscriber in self.subscribers[attribute]:
-                subscriber(Change(what=attribute,name=self._attrib_name,obj=None,cls=self._owner,old=old,new=value))
+                if self.param._changed(change):
+                    subscriber(change)
 
 
     def __get__(self,obj,objtype): # pylint: disable-msg=W0613
@@ -593,8 +595,11 @@ def __set__(self,obj,val):
             subscribers = self.subscribers.get("value",[])
         else:
             subscribers = getattr(obj,"_param_subscribers",{}).get(self._attrib_name,{}).get('value',self.subscribers.get("value",[]))
+
+        change = Change(what='value',name=self._attrib_name,obj=obj,cls=self._owner,old=_old,new=val)
         for s in subscribers:
-            s(Change(what='value',name=self._attrib_name,obj=obj,cls=self._owner,old=_old,new=val))
+            if self._owner.param._changed(change):
+                s(change)
 
 
     def __delete__(self,obj):
@@ -802,6 +807,17 @@ def inner(*args, **kwargs):
         return inner
 
 
+    @classmethod
+    def _changed(cls, change):
+        """
+        Predicate that determines whether a Change objects has actually
+        changed such that old!=new.
+        """
+        try:  # To be improve by value equality testing machinery
+            return (change.old != change.new)
+        except:
+            return True
+
     # CEBALERT: this is a bit ugly
     def _instantiate_param(self_,param_obj,dict_=None,key=None):
         # deepcopy param_obj.default into self.__dict__ (or dict_ if supplied)

tests/API1/testwatch.py

@@ -0,0 +1,43 @@
+"""
+Unit test for watch mechanism
+"""
+from . import API1TestCase
+
+import param
+
+class TestWatch(API1TestCase):
+
+    class SimpleWatchExample(param.Parameterized):
+        a = param.Integer(default=0)
+
+    def setUp(self):
+        super(TestWatch, self).setUp()
+        self.switch = False
+
+    def test_triggered_when_changed(self):
+        def switcher(*args):
+            self.switch = (not self.switch)
+
+        obj = self.SimpleWatchExample()
+        obj.param.watch(switcher, 'a')
+        obj.a = 1
+        self.assertEqual(self.switch, True)
+        obj.a = 2
+        self.assertEqual(self.switch, False)
+
+
+    def test_untriggered_when_unchanged(self):
+        def switcher(*args):
+            self.switch = (not self.switch)
+
+        obj = self.SimpleWatchExample()
+        obj.param.watch(switcher, 'a')
+        obj.a = 1
+        self.assertEqual(self.switch, True)
+        obj.a = 1
+        self.assertEqual(self.switch, True)
+
+if __name__ == "__main__":
+    import nose
+    nose.runmodule()
+