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import sys |
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sys.path.insert(0, "..") |
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import time |
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from asyncua import ua, Server |
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# INFO: The concept in this example is that the software model is first built in OPC UA via XML. After that, matching |
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# python objects are created based on the UA address space design. Do not use this example to build a UA address space |
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# from the python design. |
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# The advantage of this is that the software can be designed in a tool like UA Modeler. Then with minimal setup, a |
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# python program will import the XML and mirror all the objects in the software design. After this mirroring is achieved |
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# the user can focus on programming in python knowing that all all data from UA clients will reach the python object, |
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# and all data that needs to be output to the server can be published from the python object. |
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# |
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# Be aware that subscription calls are asynchronous. |
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class SubHandler(object): |
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""" |
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Subscription Handler. To receive events from server for a subscription. |
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The handler forwards updates to it's referenced python object |
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""" |
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def __init__(self, obj): |
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self.obj = obj |
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def datachange_notification(self, node, val, data): |
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# print("Python: New data change event", node, val, data) |
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_node_name = node.get_browse_name() |
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setattr(self.obj, _node_name.Name, data.monitored_item.Value.Value.Value) |
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class UaObject(object): |
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""" |
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Python object which mirrors an OPC UA object |
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Child UA variables/properties are auto subscribed to to synchronize python with UA server |
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Python can write to children via write method, which will trigger an update for UA clients |
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""" |
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def __init__(self, asyncua_server, ua_node): |
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self.asyncua_server = asyncua_server |
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self.nodes = {} |
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self.b_name = ua_node.get_browse_name().Name |
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# keep track of the children of this object (in case python needs to write, or get more info from UA server) |
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for _child in ua_node.get_children(): |
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_child_name = _child.get_browse_name() |
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self.nodes[_child_name.Name] = _child |
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# find all children which can be subscribed to (python object is kept up to date via subscription) |
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sub_children = ua_node.get_properties() |
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sub_children.extend(ua_node.get_variables()) |
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# subscribe to properties/variables |
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handler = SubHandler(self) |
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sub = asyncua_server.create_subscription(500, handler) |
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handle = sub.subscribe_data_change(sub_children) |
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def write_value(self, attr=None): |
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# if a specific attr isn't passed to write, write all OPC UA children |
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if attr is None: |
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for k, node in self.nodes.items(): |
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node_class = node.get_node_class() |
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if node_class == ua.NodeClass.Variable: |
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node.write_value(getattr(self, k)) |
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# only update a specific attr |
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else: |
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self.nodes[attr].write_value(getattr(self, attr)) |
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class MyObj(UaObject): |
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""" |
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Definition of OPC UA object which represents a object to be mirrored in python |
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This class mirrors it's UA counterpart and semi-configures itself according to the UA model (generally from XML) |
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""" |
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def __init__(self, asyncua_server, ua_node): |
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# properties and variables; must mirror UA model (based on browsename!) |
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self.MyVariable = 0 |
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self.MyProperty = 0 |
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self.MyClientWrite = 0 |
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# init the UaObject super class to connect the python object to the UA object |
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super().__init__(asyncua_server, ua_node) |
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88
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# local values only for use inside python |
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self.testval = 'python only' |
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91
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# If the object has other objects as children it is best to search by type and instantiate more |
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# mirrored python classes so that your UA object tree matches your python object tree |
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# ADD CUSTOM OBJECT INITIALIZATION BELOW |
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# find children by type and instantiate them as sub-objects of this class |
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# NOT PART OF THIS EXAMPLE |
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if __name__ == "__main__": |
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# setup our server |
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server = Server() |
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server.set_endpoint("opc.tcp://0.0.0.0:4840/freeopcua/server/") |
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105
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# setup our own namespace, not really necessary but should as spec |
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uri = "http://examples.freeopcua.github.io" |
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idx = server.register_namespace(uri) |
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109
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# get Objects node, this is where we should put our nodes |
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objects = server.get_objects_node() |
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112
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# populating our address space; in most real use cases this should be imported from UA spec XML |
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myobj = objects.add_object(idx, "MyObject") |
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myvar = myobj.add_variable(idx, "MyVariable", 0.0) |
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myprop = myobj.add_property(idx, "MyProperty", 0) |
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mywritevar = myobj.add_variable(idx, "MyClientWrite", 0) |
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mywritevar.set_writable() # Set MyVariable to be writable by clients |
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# starting! |
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server.start() |
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122
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# after the UA server is started initialize the mirrored object |
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my_python_obj = MyObj(server, myobj) |
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125
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try: |
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while True: |
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# from an OPC UA client write a value to this node to see it show up in the python object |
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print('Python mirror of MyClientWrite is: ' + str(my_python_obj.MyClientWrite)) |
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130
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# write a single attr to OPC UA |
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my_python_obj.MyVariable = 12.3 |
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my_python_obj.MyProperty = 55 # this value will not be visible to clients because write is not called |
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my_python_obj.write_value('MyVariable') |
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time.sleep(3) |
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# write all attr of the object to OPC UA |
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my_python_obj.MyVariable = 98.1 |
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my_python_obj.MyProperty = 99 |
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my_python_obj.write_value() |
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time.sleep(3) |
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144
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# write directly to the OPC UA node of the object |
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dv = ua.DataValue(ua.Variant(5.5, ua.VariantType.Double)) |
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my_python_obj.nodes['MyVariable'].write_value(dv) |
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dv = ua.DataValue(ua.Variant(4, ua.VariantType.UInt64)) |
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my_python_obj.nodes['MyVariable'].write_value(dv) |
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time.sleep(3) |
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finally: |
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# close connection, remove subscriptions, etc |
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server.stop() |
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FreeOpcUa /
opcua-asyncio
