Ensure that param watch decorator is resolved using MRO (#327)

param/parameterized.py

@@ -2246,14 +2246,17 @@ def __init__(self,**params):
         object_count += 1
 
         # add watched dependencies
-        for n in self.__class__.param._depends['watch']:
-            # TODO: should improve this - will happen for every
-            # instantiation of Parameterized with watched deps. Will
-            # probably store expanded deps on class - see metaclass
-            # 'dependers'.
-            for p in self.param.params_depended_on(n):
-                # TODO: can't remember why not just pass m (rather than _m_caller) here
-                (p.inst or p.cls).param.watch(_m_caller(self,n),p.name,p.what)
+        for cls in classlist(self.__class__):
+            if not issubclass(cls, Parameterized):
+                continue
+            for n in cls.param._depends['watch']:
+                # TODO: should improve this - will happen for every
+                # instantiation of Parameterized with watched deps. Will
+                # probably store expanded deps on class - see metaclass
+                # 'dependers'.
+                for p in self.param.params_depended_on(n):
+                    # TODO: can't remember why not just pass m (rather than _m_caller) here
+                    (p.inst or p.cls).param.watch(_m_caller(self,n),p.name,p.what)
 
         self.initialized=True
 

tests/API1/testwatch.py

@@ -55,6 +55,11 @@ def _set_d_bounds(self):
         self.param.d.bounds = (self.c, self.c*2)
 
 
+class WatchSubclassExample(WatchMethodExample):
+
+    pass
+
+
 
 class TestWatch(API1TestCase):
 
@@ -451,6 +456,13 @@ def test_multiple_watcher_dispatch_on_param_attribute(self):
         self.assertEqual(obj.param.d.bounds, (2, 4))
         self.assertEqual(accumulator.call_count(), 1)
 
+    def test_depends_with_watch_on_subclass(self):
+        obj = WatchSubclassExample()
+
+        obj.b = 3
+        self.assertEqual(obj.c, 6)
+
+
 
 
 class TestWatchValues(API1TestCase):