dataclasses.FrozenInstanceError: cannot assign to field 'SourceTimestamp'/ 'ServerTimestamp'

[Alfy102]

Hello again,

I have encountered an error as per title. I was implementing this along with the solution:
https://github.com/FreeOpcUa/opcua-asyncio/discussions/604#discussion-3401447

This is because everytime the server write_attribute_value, no ServerTimeStamp was recorded or rather it always shows in UA Expert as 8AM 1/1/1601 after every write. Hence I forced the data_value.SourceTimestamp = datetime.now().

My code:

async def rw_opc(nodes_id,data_list,server):
if isinstance(nodes_id,list):
        for i in range(len(nodes_id)):
            data_value = ua.DataValue(bool(int(data_list[i])))
            data_value.SourceTimestamp = datetime.now()
            await server.write_attribute_value(nodes_id[i].nodeid, data_value,attr=ua.AttributeIds.Value)
            #nodes_id[i].set_value(data_value)
    else:
        data_value = ua.DataValue(bool(int(data_list)))
        data_value.SourceTimestamp = datetime.now()
        await server.write_attribute_value(nodes_id.nodeid, data_value,attr=ua.AttributeIds.Value)
        #nodes_id.set_value(data_value)

The error:

    data_value.SourceTimestamp = datetime.now()
  File "<string>", line 4, in __setattr__
dataclasses.FrozenInstanceError: cannot assign to field 'SourceTimestamp'
Exception ignored in: <function _ProactorBasePipeTransport.__del__ at 0x000001B4BB425940>

Your time is much appreciated.

[Alfy102]

Just found out if I don't await rw_opc the error does not occur and it writes the time to SourceTimestamp when looking through UA Expert. However none of my Nodes get any data_value written.

[Alfy102]

Solved.

added ServerTimestamp = datetime.now() like this:

data_value = ua.DataValue(bool(int(data_list[i])), ServerTimestamp=datetime.now())

and remove data_value.SourceTimestamp = datetime.now()