How to use the sysrepo.SR_ERR_OK function in sysrepo

oper_status.reset(sr.Data_Node(ifc, mod, "oper-status", "up"));

        ifc.reset(sr.Data_Node(parent, mod, "interface"));
        name.reset(sr.Data_Node(ifc, mod, "name", "eth102"));
        typ.reset(sr.Data_Node(ifc, mod, "type", "iana-if-type:ethernetCsmacd"));
        oper_status.reset(sr.Data_Node(ifc, mod, "oper-status", "dormant"));

        ifc.reset(sr.Data_Node(parent, mod, "interface"));
        name.reset(sr.Data_Node(ifc, mod, "name", "eth105"));
        typ.reset(sr.Data_Node(ifc, mod, "type", "iana-if-type:ethernetCsmacd"));
        oper_status.reset(sr.Data_Node(ifc, mod, "oper-status", "not-present"));

    except Exception as e:
        print (e)
        return sr.SR_ERR_OK
    return sr.SR_ERR_OK

def oper_get_items_cb2(session, module_name, path, request_xpath, request_id, parent, private_data):
    print ("\n\n ========== CALLBACK CALLED TO PROVIDE \"" + path + "\" DATA ==========\n")
    try:
        ctx = session.get_context()
        mod = ctx.get_module(module_name)

        stats = sr.Data_Node(parent, mod, "statistics")
        dis_time = sr.Data_Node(stats, mod, "discontinuity-time", "2019-01-01T00:00:00Z")
        in_oct = sr.Data_Node(stats, mod, "in-octets", "22")

    except Exception as e:
        print (e)
        return sr.SR_ERR_OK
    return sr.SR_ERR_OK

change_path = "/" + module_name + ":*//."

        it = sess.get_changes_iter(change_path);

        while True:
            change = sess.get_change_next(it)
            if change == None:
                break
            print_change(change.oper(), change.old_val(), change.new_val())

        print ("\n\n ========== END OF CHANGES =======================================\n")

    except Exception as e:
        print (e)

    return sr.SR_ERR_OK

def module_change_cb(sess, module_name, xpath, event, request_id, private_data):
    print ("\n\n ========== CONFIG HAS CHANGED, CURRENT RUNNING CONFIG: ==========\n")

    print_current_config(sess, module_name)

    return sr.SR_ERR_OK