OPC UA调用含双输入参数的方法报错求助

Hey there, no worries at all about basic questions—we all start somewhere! Let's work through this method call issue together.

First, let's break down why your two attempts are failing:

• When you pass 1, 20 directly, you get BadInvalidArgument because OPC UA is a strongly typed protocol. Python's native int might not match the exact data type the SetDefault method expects (like UInt32, Int16, etc.).
• When you wrap them in a list [1,20], the method interprets the entire list as the first argument, leaving the second argument missing—hence the BadArgumentsMissing error.

Here's how to fix it: #

1. First, confirm the exact data types of the method's input parameters

In UaExpert, navigate to the SetDefault method, expand its InputArguments property. You'll see each parameter's DataType (e.g., UInt32, Int64, Float). Note these types down.

2. Wrap your parameters in matching OPC UA types

Use the opcua library's built-in type classes or Variant objects to match the expected data types. Here are two reliable approaches:

Approach 1: Explicitly use OPC UA type objects

If you know the exact types from UaExpert, directly create instances of those types:

import opcua as ua

# Initialize your client first (code omitted)

evse = client.get_node("ns=6;s=::EVSE")
set_default = client.get_node("ns=6;s=::EVSE:SetDefault")

# Replace with the actual types from UaExpert
arg1 = ua.UInt32(1)  # Example: if first param is UInt32
arg2 = ua.UInt16(20) # Example: if second param is UInt16

res = evse.call_method(set_default, arg1, arg2)

Approach 2: Dynamically match the method's expected types

If you want a more flexible solution that auto-detects the required types:

import opcua as ua

# Initialize your client first (code omitted)

evse = client.get_node("ns=6;s=::EVSE")
set_default = client.get_node("ns=6;s=::EVSE:SetDefault")

# Fetch the method's input parameter metadata
input_args_meta = set_default.get_child(["0:InputArguments"]).get_value()

# Build arguments with matching data types
arguments = []
arguments.append(ua.Variant(1, input_args_meta[0].DataType))
arguments.append(ua.Variant(20, input_args_meta[1].DataType))

# Unpack the arguments when calling the method
res = evse.call_method(set_default, *arguments)

Why this works: #

OPC UA doesn't automatically convert Python native types to the correct OPC UA types. By explicitly wrapping your values in the matching type (either via the type class or Variant), you ensure the server receives arguments that match its expected schema—just like when you call the method manually in UaExpert.

内容的提问来源于stack exchange，提问作者Dave