Ensure toggled Accordion only triggers one event on change of active …

…Card (#2934)

panel/layout/accordion.py

@@ -118,15 +118,20 @@ def _apply_style(self, i):
     def _set_active(self, *events):
         if self._updating_active:
             return
-        active = []
         self._updating_active = True
         try:
-            for i, pane in enumerate(self.objects):
-                if id(pane) not in self._panels:
-                    continue
-                elif not self._panels[id(pane)].collapsed:
-                    active.append(i)
-            self.active = active
+            if self.toggle and not events[0].new:
+                active = [list(self._panels.values()).index(events[0].obj)]
+            else:
+                active = []
+                for i, pane in enumerate(self.objects):
+                    if id(pane) not in self._panels:
+                        continue
+                    elif not self._panels[id(pane)].collapsed:
+                        active.append(i)
+
+            if not self.toggle or active:
+                self.active = active
         finally:
             self._updating_active = False
 

panel/tests/layout/test_accordion.py

@@ -126,14 +126,45 @@ def test_accordion_active(document, comm, accordion):
 def test_accordion_set_card_collapsed(document, comm, accordion):
     accordion.get_root(document, comm=comm)
 
+    events = []
+
+    accordion.param.watch(lambda e: events.append(e), 'active')
+
     c1, c2 = accordion._panels.values()
 
     c1.collapsed = False
     assert accordion.active == [0]
 
+    assert len(events) == 1
+
     c2.collapsed = False
     assert accordion.active == [0, 1]
 
+    assert len(events) == 2
+
     c1.collapsed = True
     c2.collapsed = True
     assert accordion.active == []
+
+    assert len(events) == 4
+
+
+def test_accordion_set_card_collapsed_toggle(document, comm, accordion):
+    accordion.toggle = True
+    accordion.get_root(document, comm=comm)
+
+    events = []
+
+    accordion.param.watch(lambda e: events.append(e), 'active')
+
+    c1, c2 = accordion._panels.values()
+
+    c1.collapsed = False
+    assert accordion.active == [0]
+
+    assert len(events) == 1
+
+    c2.collapsed = False
+    assert accordion.active == [1]
+
+    assert len(events) == 2