Python implements OPCUA client and server

python opc ua client and server case

1. Install the python-opcua component

pip install opcua

2. Python opcua server server production data case :

Server

from threading import Thread
import copy
import logging
from datetime import datetime
import time
from math import sin
import sys
sys.path.insert(0, "..")

try:
    from IPython import embed
except ImportError:
    import code

    def embed():
        myvars = globals()
        myvars.update(locals())
        shell = code.InteractiveConsole(myvars)
        shell.interact()


from opcua import ua, uamethod, Server


class SubHandler(object):

    """
 Subscription Handler. To receive events from server for a subscription
 """

    def datachange\_notification(self, node, val, data):
        print("Python: New data change event", node, val)

    def event\_notification(self, event):
        print("Python: New event", event)


# method to be exposed through server

def func(parent, variant):
    ret = False
    if variant.Value % 2 == 0:
        ret = True
    return [ua.Variant(ret, ua.VariantType.Boolean)]


# method to be exposed through server
# uses a decorator to automatically convert to and from variants

@uamethod
def multiply(parent, x, y):
    print("multiply method call with parameters: ", x, y)
    return x * y


class VarUpdater(Thread):
    def \_\_init\_\_(self, var):
        Thread.__init__(self)
        self._stopev = False
        self.var = var

    def stop(self):
        self._stopev = True

    def run(self):
        while not self._stopev:
            v = sin(time.time() / 10)
            self.var.set_value(v)
            time.sleep(0.1)



if __name__ == "\_\_main\_\_":
    # optional: setup logging
    logging.basicConfig(level=logging.WARN)
    #logger = logging.getLogger("opcua.address\_space")
    # logger.setLevel(logging.DEBUG)
    #logger = logging.getLogger("opcua.internal\_server")
    # logger.setLevel(logging.DEBUG)
    #logger = logging.getLogger("opcua.binary\_server\_asyncio")
    # logger.setLevel(logging.DEBUG)
    #logger = logging.getLogger("opcua.uaprocessor")
    # logger.setLevel(logging.DEBUG)

    # now setup our server
    server = Server()
    #server.disable\_clock()
    #server.set\_endpoint("opc.tcp://localhost:4840/freeopcua/server/")
    server.set_endpoint("opc.tcp://0.0.0.0:4841/freeopcua/server/")
    server.set_server_name("FreeOpcUa Example Server")
    # set all possible endpoint policies for clients to connect through
    server.set_security_policy([
        ua.SecurityPolicyType.NoSecurity,
        # ua.SecurityPolicyType.Basic256Sha256\_SignAndEncrypt,
        # ua.SecurityPolicyType.Basic256Sha256\_Sign
    ])

    # setup our own namespace
    uri = "http://examples.freeopcua.github.io"
    idx = server.register_namespace(uri)

    # create a new node type we can instantiate in our address space
    dev = server.nodes.base_object_type.add_object_type(0, "MyDevice")
    dev.add_variable(0, "sensor1", 1.0).set_modelling_rule(True)
    dev.add_property(0, "device\_id", "0340").set_modelling_rule(True)
    ctrl = dev.add_object(0, "controller")
    ctrl.set_modelling_rule(True)
    ctrl.add_property(0, "state", "Idle").set_modelling_rule(True)

    # populating our address space

    # First a folder to organise our nodes
    myfolder = server.nodes.objects.add_folder(idx, "myEmptyFolder")
    # instanciate one instance of our device
    mydevice = server.nodes.objects.add_object(idx, "Device0001", dev)
    mydevice_var = mydevice.get_child(["0:controller", "0:state"])  # get proxy to our device state variable 
    # create directly some objects and variables
    myobj = server.nodes.objects.add_object(idx, "MyObject")
    myvar = myobj.add_variable(idx, "MyVariable", 6.7)
    mysin = myobj.add_variable(idx, "MySin", 0, ua.VariantType.Float)
    myvar.set_writable()    # Set MyVariable to be writable by clients
    mystringvar = myobj.add_variable(idx, "MyStringVariable", "Really nice string")
    mystringvar.set_writable()    # Set MyVariable to be writable by clients
    mydtvar = myobj.add_variable(idx, "MyDateTimeVar", datetime.utcnow())
    mydtvar.set_writable()    # Set MyVariable to be writable by clients
    myarrayvar = myobj.add_variable(idx, "myarrayvar", [6.7, 7.9])
    myarrayvar = myobj.add_variable(idx, "myStronglytTypedVariable", ua.Variant([], ua.VariantType.UInt32))
    myprop = myobj.add_property(idx, "myproperty", "I am a property")
    mymethod = myobj.add_method(idx, "mymethod", func, [ua.VariantType.Int64], [ua.VariantType.Boolean])
    multiply_node = myobj.add_method(idx, "multiply", multiply, [ua.VariantType.Int64, ua.VariantType.Int64], [ua.VariantType.Int64])

    # import some nodes from xml
    # server.import\_xml("custom\_nodes.xml")

    # creating a default event object
    # The event object automatically will have members for all events properties
    # you probably want to create a custom event type, see other examples
    myevgen = server.get_event_generator()
    myevgen.event.Severity = 300

    # starting!
    server.start()
    print("Available loggers are: ", logging.Logger.manager.loggerDict.keys())
    vup = VarUpdater(mysin)  # just a stupide class update a variable
    vup.start()
    try:
        # enable following if you want to subscribe to nodes on server side
        #handler = SubHandler()
        #sub = server.create\_subscription(500, handler)
        #handle = sub.subscribe\_data\_change(myvar)
        # trigger event, all subscribed clients wil receive it
        var = myarrayvar.get_value()  # return a ref to value in db server side! not a copy!
        var = copy.copy(var)  # WARNING: we need to copy before writting again otherwise no data change event will be generated
        var.append(9.3)
        myarrayvar.set_value(var)
        mydevice_var.set_value("Running")
        myevgen.trigger(message="This is BaseEvent")
        server.set_attribute_value(myvar.nodeid, ua.DataValue(9.9))  # Server side write method which is a but faster than using set\_value

        embed()
    finally:
        vup.stop()
        server.stop()

This service program demonstrates almost all the functions of the opcua server, and the Event part is not sent continuously, so it is for reference only.

The following figure shows the object structure on the server side

3. python opcua client client read data case

client

from IPython import embed
from opcua import Client

class SubHandler(object):
    def event\_notification(self, event):
        print("Event:", event.EventId, event.Time, event.proper_random, event.Message.Text)

def main\_c():
    url = "opc.tcp://127.0.0.1:4841/freeopcua/server/"
    c = Client(url)
    try:
        c.connect()
        root = c.get_root_node()
        embed()
    except Exception as e:
        print("Client Exception:", e)
    finally:
        c.disconnect()
        
if __name__ == "\_\_main\_\_":
    main_c()

Client traversal process:

1. Get all the child nodes of the node rootbelow Objects, the general type is Object, take one as A
2. Get the sum of A NodeClass(usually Object) TypeDefinition, where NodeId needs ["0:Types","0:ObjectTypes","0:BaseObjectType"]to be compared with the type under the path (including custom types).
3. Continue to use A as the root and traverse the child nodes. If it is Object, continue to 2. If yes Variable, compare NodeId ["0:Types","0:VariableTypes","0:BaseVariableType"]to determine whether it is a variable (variable, 63) or a property (property, 65).
4. For Methoduse a_root.call_method(a, arg1)calls. For Variableuse get_value/get_data_value()get the stored value. If yes Objectcontinue to 2.
5. For Variableuse access_levelto get whether there is write permission, if so, set_valueyou can set the value.

A more perfect traversal client:

from opcua import Client, ua


def brower\_child(root):
    """
 递归调用遍历，格式化不好做，有深度问题
 """
    name = root.get_node_class().name
    # print(name)
    if name == "Object":
        brower_obj(root)
        for c in root.get_children():
            print(" ", end='')
            brower_child(c)
    elif name == 'Variable':
        brower_var(root)
    else:
        brower_method(root)


class CurState():
    def \_\_init\_\_(self, parent=None, p=None, d=0):
        self.parent = parent  # unused
        self.p = p
        self.d = d


def brower\_child2(root, max_d=-1, ignore=[]):
    """
 栈+循环遍历，非常好用
 """
    stack = [CurState(None, root, 0)]
    while len(stack):
        cur = stack.pop()
        name = cur.p.get_node_class().name

        print(''.join([' ' for i in range(cur.d)]), end="")

        if cur.p.get_browse_name().Name in ignore:
            continue

        if name == "Object":
            brower_obj(cur.p)
            if max_d > 0 and cur.d >= max_d:
                continue
            for c in cur.p.get_children():
                stack.append(CurState(cur.p, c, cur.d+1))

        elif name == 'Variable':
            brower_var(cur.p)
        else:
            brower_method(cur.p)


def brower\_obj(v):
    # print(v.get\_browse\_name())
    rw = 'R '
    bname = v.get_browse_name()
    print("*%2d:%-30s (%-2s, %-23s)" %
          (bname.NamespaceIndex, bname.Name, rw, "Object"))


def brower\_var(v):
    # print(v.get\_browse\_name())
    rw = 'R '
    if ua.AccessLevel.CurrentWrite in v.get_access_level():
        rw = "RW"
    bname = v.get_browse_name()
    tv = v.get_data_value().Value
    v_show = tv.Value
    if len(str(v_show)) > 1024:
        v_show = str(v_show[:56]) + "..."
    print("-%2d:%-30s (%-2s, %-23s) =>" %
          (bname.NamespaceIndex, bname.Name, rw, tv.VariantType), v_show)


def brower\_method(v):
    # print(v.get\_description())
    rw = 'C '
    bname = v.get_browse_name()
    # args = []
    # for a in v.get\_properties():
    # dt = a.get\_data\_type().NodeIdType.name
    # args.append(dt)
    print("@%2d:%-30s (%-2s, %-23s)" %
          (bname.NamespaceIndex, bname.Name, rw, "Method"))


def main\_c():
    url = "opc.tcp://127.0.0.1:4841/freeopcua/server/"
    c = Client(url)
    try:
        c.connect()
        root = c.get_root_node()
        print("\r\nBrower:")
        brower_child2(root.get_child(["0:Objects"]), -1, ["Server"])
    except Exception as e:
        print("Client Exception:", e)
    finally:
        c.disconnect()


if __name__ == "\_\_main\_\_":
    main_c()

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