Graceful fallback for non-existing OPC-UA nodes, and moved connect logic to dedicated function

RCUSCC/RCUSCC/RCUSCC.py

@@ -160,7 +160,36 @@ class RCUSCC(Device):
     # ---------------
 
     def get_pcc_node(self, node):
-        return self.pcc_node.get_child(["{}:{}".format(self.name_space_index, node)])
+        try:
+            return self.pcc_node.get_child(["{}:{}".format(self.name_space_index, node)])
+        except opcua.ua.uaerrors._auto.BadNoMatch:
+            self.error_stream("Could not find PCC node %s, using a dummy", node)
+
+            class DummyNode:
+                def get_value(self):
+                    pass
+
+                def set_value(self, val):
+                    pass
+
+            return DummyNode()
+
+
+    def _connect(self):
+        self.debug_stream("Connecting to OPC-UA server %s:%d...", self.OPC_Server_Name, self.OPC_Server_Port)
+
+        self.client = opcua.Client("opc.tcp://{}:{}/".format(self.OPC_Server_Name, self.OPC_Server_Port), self.OPC_Time_Out * 1000)
+        self.client.connect()
+        self.debug_stream("Connecting to OPC-UA server %s:%d done.", self.OPC_Server_Name, self.OPC_Server_Port)
+
+        try:
+            self.name_space_index = self.client.get_namespace_index("http://lofar.eu")
+        except Exception as e:
+            self.warn_stream("Cannot determine the OPC-UA name space index.  Will try and use the default = 2.")
+            self.name_space_index = 2
+
+        self.obj_node = self.client.get_objects_node()
+        self.pcc_node = self.obj_node.get_child(["{}:PCC".format(self.name_space_index)])
 
 
     def init_device(self):
@@ -211,20 +240,7 @@ class RCUSCC(Device):
         # Set defaults to property values.
 
         try:
-            self.debug_stream("Connecting to OPC-UA server %s:%d...", self.OPC_Server_Name, self.OPC_Server_Port)
-
-            self.client = opcua.Client("opc.tcp://{}:{}/".format(self.OPC_Server_Name, self.OPC_Server_Port), self.OPC_Time_Out * 1000)
-            self.client.connect()
-            self.debug_stream("Connecting to OPC-UA server %s:%d done.", self.OPC_Server_Name, self.OPC_Server_Port)
-
-            try:
-                self.name_space_index = self.client.get_namespace_index("http://lofar.eu")
-            except Exception as e:
-                self.warn_stream("Cannot determine the OPC-UA name space index.  Will try and use the default = 2.")
-                self.name_space_index = 2
-
-            self.obj_node = self.client.get_objects_node()
-            self.pcc_node = self.obj_node.get_child(["{}:PCC".format(self.name_space_index)])
+            self._connect()
 
             self.debug_stream("Mapping OPC-UA MP/CP to attributes...")