在 python 客户端中获取 OPC UA 数组对象值（Byte、UInt16）

问：

我正在创建一个基于 opcua-asyncio github （https://github.com/FreeOpcUa/opcua-asyncio） 的 python OPC UA 客户端，以读取已设置服务器的仪器中的值。

我的问题在于读取数据类型 byte 或 UInt16 的数组值。 我期望的是类似于下面 UaExpert/DataFeed 中显示的值。

UaExpert 字节数组

但是，如果我使用 python 客户端，我会在每个变体对象中得到 Value = 0。

val:  [Variant(Value=0, VariantType=<VariantType.UInt16: 5>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.UInt16: 5>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.UInt16: 5>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.UInt16: 5>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.UInt16: 5>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.UInt16: 5>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.UInt16: 5>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.UInt16: 5>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.UInt16: 5>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.UInt16: 5>, Dimensions=None, is_array=False)]

val:  [Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False)]

我也尝试了一些其他功能，结果如下。

import asyncio
import logging
import sys
import common
from asyncua import ua

sys.path.insert(0, "..")

async def main():
    client = await common.connectViaUsername()
    try:
        async with client:
            while True:
                # Getting a variable nodes
                pi_node = client.get_node("ns=1;i=57")

                val = await pi_node.read_value()

                print("val: ", val)
                print("type of val: ", type(val))

                att = await pi_node.read_attribute(ua.AttributeIds.DataType)
                print("att: ", att)
                print("type of att: ", type(att))
                print("att value value: ", att.Value.Value)

                dataval = await pi_node.read_data_value()
                print("dataval: ", dataval)
                print("variant type: ", dataval.Value.Value[0].VariantType)

                rv = ua.ReadValueId()
                rv.NodeId = pi_node.nodeid
                rv.AttributeId = ua.AttributeIds.DataType
                params = ua.ReadParameters()
                params.NodesToRead.append(rv)
                result = await pi_node.session.read(params)
                print("result: ", result)
                print(type(result[0]))
                print(type(result[0].Value))
                print(type(result[0].data_type))
                print(type(result[0].Encoding))
                print((result[0].Value))
                print((result[0].data_type))
                print((result[0].Encoding))

                print("node_class: ", await pi_node.read_node_class())
                print("att.value: ", await pi_node.read_attribute(ua.AttributeIds.Value))
                print("data type: ", await pi_node.read_data_type())
                print("array dim: ", await pi_node.read_array_dimensions())
                print("data values: ", await pi_node.read_data_value())
                print("variant type: ", await pi_node.read_data_type_as_variant_type())
                print("_______")

                await asyncio.sleep(100)
    except ua.UaError as err:
        _logger.error(err)
    finally:
        await client.disconnect()


if __name__ == "__main__":
    logging.basicConfig(level=logging.INFO)  # configure at info level
    _logger = logging.getLogger(__name__)

    # filter out the logs from asynua logger
    logging.getLogger('asyncua').setLevel(logging.CRITICAL + 1)

    # formate log messages with the file path of the log, comment out if not needed
    fh = common.configureLogs("logs/OPC Status - InstrumentSensor (Pulse Sensors).log")
    _logger.addHandler(fh)

    asyncio.run(main())

这些是 print 语句的结果。

val:  [Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False)]
type of val:  <class 'list'>
att:  DataValue(Value=Variant(Value=NodeId(Identifier=3, NamespaceIndex=0, NodeIdType=<NodeIdType.TwoByte: 0>), VariantType=<VariantType.NodeId: 17>, Dimensions=None, is_array=False), StatusCode_=StatusCode(value=0), SourceTimestamp=None, ServerTimestamp=None, SourcePicoseconds=None, ServerPicoseconds=None)
type of att:  <class 'asyncua.ua.uatypes.DataValue'>
att value value:  NodeId(Identifier=3, NamespaceIndex=0, NodeIdType=<NodeIdType.TwoByte: 0>)
dataval:  DataValue(Value=Variant(Value=[Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False)], VariantType=<VariantType.Variant: 24>, Dimensions=None, is_array=True), StatusCode_=StatusCode(value=0), SourceTimestamp=datetime.datetime(2023, 10, 27, 1, 48, 35, 270000), ServerTimestamp=None, SourcePicoseconds=None, ServerPicoseconds=None)
variant type:  VariantType.Byte
result:  [DataValue(Value=Variant(Value=NodeId(Identifier=3, NamespaceIndex=0, NodeIdType=<NodeIdType.TwoByte: 0>), VariantType=<VariantType.NodeId: 17>, Dimensions=None, is_array=False), StatusCode_=StatusCode(value=0), SourceTimestamp=None, ServerTimestamp=None, SourcePicoseconds=None, ServerPicoseconds=None)]
<class 'asyncua.ua.uatypes.DataValue'>
<class 'asyncua.ua.uatypes.Variant'>
<class 'asyncua.ua.uatypes.NodeId'>
<class 'int'>
Variant(Value=NodeId(Identifier=3, NamespaceIndex=0, NodeIdType=<NodeIdType.TwoByte: 0>), VariantType=<VariantType.NodeId: 17>, Dimensions=None, is_array=False)
NodeId(Identifier=25, NamespaceIndex=0, NodeIdType=<NodeIdType.TwoByte: 0>)
0
node_class:  2
att.value:  DataValue(Value=Variant(Value=[Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False)], VariantType=<VariantType.Variant: 24>, Dimensions=None, is_array=True), StatusCode_=StatusCode(value=0), SourceTimestamp=datetime.datetime(2023, 10, 27, 1, 48, 35, 270000), ServerTimestamp=None, SourcePicoseconds=None, ServerPicoseconds=None)
data type:  NodeId(Identifier=3, NamespaceIndex=0, NodeIdType=<NodeIdType.TwoByte: 0>)
array dim:  [10]
data values:  DataValue(Value=Variant(Value=[Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False), Variant(Value=0, VariantType=<VariantType.Byte: 3>, Dimensions=None, is_array=False)], VariantType=<VariantType.Variant: 24>, Dimensions=None, is_array=True), StatusCode_=StatusCode(value=0), SourceTimestamp=datetime.datetime(2023, 10, 27, 1, 48, 35, 270000), ServerTimestamp=None, SourcePicoseconds=None, ServerPicoseconds=None)
variant type:  VariantType.Byte

我的想法是 python 客户端正在将 byte/UInt16 值解码为值为 0 的 int，因为它无法打印这样的 bytes/UInt16。

注意：我能够毫无问题地读取字符串/浮点数组。下面是浮点数组的示例

[Variant(Value=1002.32, VariantType=<VariantType.Double: 11>, Dimensions=None, is_array=False), Variant(Value=1002.01, VariantType=<VariantType.Double: 11>, Dimensions=None, is_array=False), Variant(Value=1002.16, VariantType=<VariantType.Double: 11>, Dimensions=None, is_array=False), Variant(Value=1002.4, VariantType=<VariantType.Double: 11>, Dimensions=None, is_array=False), Variant(Value=0.0, VariantType=<VariantType.Double: 11>, Dimensions=None, is_array=False), Variant(Value=0.0, VariantType=<VariantType.Double: 11>, Dimensions=None, is_array=False), Variant(Value=0.0, VariantType=<VariantType.Double: 11>, Dimensions=None, is_array=False), Variant(Value=0.0, VariantType=<VariantType.Double: 11>, Dimensions=None, is_array=False), Variant(Value=0.0, VariantType=<VariantType.Double: 11>, Dimensions=None, is_array=False), Variant(Value=0.0, VariantType=<VariantType.Double: 11>, Dimensions=None, is_array=False)]

有什么方法可以读取 byte/UInt16 数组值？

此致敬意 opc 初学者