Fixed issue setting (Multi)Select value when options changed (#291)

* Skip setting unavailable values

* Fixed issue setting (Multi)Select value when options changed

panel/tests/test_widgets.py

@@ -269,6 +269,22 @@ def test_select_mutables(document, comm):
     assert widget.value == 'A'
 
 
+def test_select_change_options(document, comm):
+    select = Select(options=OrderedDict([('A', 'A'), ('1', 1), ('C', object)]),
+                         value='A', name='Select')
+
+    def set_options(event):
+        if event.new == 1:
+            select.options = OrderedDict([('D', 2), ('E', 'a')])
+    select.param.watch(set_options, 'value')
+
+    model = select._get_root(document, comm=comm)
+
+    select.value = 1
+    assert model.value == 'D'
+    assert model.options == ['D', 'E']
+
+
 def test_multi_select(document, comm):
     select = MultiSelect(options=OrderedDict([('A', 'A'), ('1', 1), ('C', object)]),
                          value=[object, 1], name='Select')
@@ -292,6 +308,22 @@ def test_multi_select(document, comm):
     assert widget.value == ['C', 'A']
 
 
+def test_multi_select_change_options(document, comm):
+    select = MultiSelect(options=OrderedDict([('A', 'A'), ('1', 1), ('C', object)]),
+                         value=[object, 1], name='Select')
+
+    def set_options(event):
+        if event.new == [1]:
+            select.options = OrderedDict([('D', 2), ('E', 'a')])
+    select.param.watch(set_options, 'value')
+
+    model = select._get_root(document, comm=comm)
+
+    select.value = [1]
+    assert model.value == []
+    assert model.options == ['D', 'E']
+
+
 def test_toggle_group_error_init(document, comm):
     with pytest.raises(ValueError):
         ToggleGroup(options=OrderedDict([('A', 'A'), ('1', 1), ('C', object)]),

panel/widgets/select.py

@@ -45,15 +45,22 @@ def _process_param_change(self, msg):
         msg = super(Select, self)._process_param_change(msg)
         mapping = {hashable(v): k for k, v in self.options.items()}
         if msg.get('value') is not None:
-            msg['value'] = mapping[hashable(msg['value'])]
+            hash_val = hashable(msg['value'])
+            if hash_val in mapping:
+                msg['value'] = mapping[hash_val]
+            else:
+                msg['value'] = list(self.options)[0]
         if 'options' in msg:
             msg['options'] = list(msg['options'])
         return msg
 
     def _process_property_change(self, msg):
         msg = super(Select, self)._process_property_change(msg)
         if 'value' in msg:
-            msg['value'] = self.options[msg['value']]
+            if msg['value'] is None:
+                msg['value'] = None
+            else:
+                msg['value'] = self.options[msg['value']]
         msg.pop('options', None)
         return msg
 
@@ -72,7 +79,8 @@ def _process_param_change(self, msg):
         msg = super(Select, self)._process_param_change(msg)
         mapping = {hashable(v): k for k, v in self.options.items()}
         if 'value' in msg:
-            msg['value'] = [hashable(mapping[v]) for v in msg['value']]
+            msg['value'] = [hashable(mapping[v]) for v in msg['value']
+                            if v in mapping]
         if 'options' in msg:
             msg['options'] = list(msg['options'])
         return msg