methods.py

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"""
High level method related functions
"""

from opcua import ua
from opcua.common import node


def call_method(parent, methodid, *args):
    """
    Call an OPC-UA method. methodid is browse name of child method or the
    nodeid of method as a NodeId object
    arguments are variants or python object convertible to variants.
    which may be of different types
    returns a list of variants which are output of the method
    """
    if isinstance(methodid, str):
        methodid = parent.get_child(methodid).nodeid
    elif isinstance(methodid, node.Node):
        methodid = methodid.nodeid

    arguments = []
    for arg in args:
        if not isinstance(arg, ua.Variant):
            arg = ua.Variant(arg)
        arguments.append(arg)

    result = _call_method(parent.server, parent.nodeid, methodid, arguments)

    if len(result.OutputArguments) == 0:
        return None
    elif len(result.OutputArguments) == 1:
        return result.OutputArguments[0].Value
    else:
        return [var.Value for var in result.OutputArguments]


def _call_method(server, parentnodeid, methodid, arguments):
    request = ua.CallMethodRequest()
    request.ObjectId = parentnodeid
    request.MethodId = methodid
    request.InputArguments = arguments
    methodstocall = [request]
    results = server.call(methodstocall)
    res = results[0]
    res.StatusCode.check()
    return res


def uamethod(func):
    """
    Method decorator to automatically convert
    arguments and output to and from variants
    """
    def wrapper(parent, *args):
        if isinstance(parent, ua.NodeId):
            result = func(parent, *[arg.Value for arg in args])
        else:
            self = parent
            parent = args[0]
            args = args[1:]
            result = func(self, parent, *[arg.Value for arg in args])

        return to_variant(result)
    return wrapper


def to_variant(*args):
    uaargs = []
    for arg in args:
        uaargs.append(ua.Variant(arg))
    return uaargs