Interactive Browser¶

Walks the server's address space from a terminal using the high-level Client.browseInteractive() helper. The browser is a terminal UI: arrow keys (or h/j/k/l) move through the children of the current node, Enter drills into a child, h / Backspace goes back up the tree, / filters children by a fuzzy substring match, and q quits.

browseInteractive() is the only entry point. When the user quits with Enter on a child, a small dialog asks whether to return the NodeId of the selected node or a BrowsePath slash-delimited string. browseInteractive() then returns that string. The return value is the part of the API a script can plug into a follow-up client.read(returned_string) call without re-walking the tree.

The example targets S03_firststeps.py. browseInteractive() requires the standard-library curses module (on Windows, install windows-curses).

python examples/server/S03_firststeps.py

The interactive browser is a wrapper around the same Browse service that client.browse() and client[NodeId] use. It just caches the result in an UI instead of returning Python objects.

1. Endpoint and starting node¶

The endpoint URL matches the convention used by every other example in this directory. The starting NodeId is optional: when omitted the browser opens at the root (i=0). Pass any NodeId as a CLI argument to start somewhere else — for example the Objects folder "i=85", a specific sensor on S03_firststeps.py like "ns=1;i=1001", or any other node you want to inspect.

localhost = "localhost"
endpoint_url = f"opc.tcp://{localhost}:4840"

start_nodeid: str | None = None
if len(sys.argv) > 1:
    start_nodeid = sys.argv[1]
    print(f"Starting browser at {start_nodeid}")
else:
    print("Starting browser at the address-space root (pass a NodeId to start elsewhere)")

2. Connect and launch the browser¶

The browser takes over the terminal until the user quits, so we connect first, run the browser inside a with block, and let __exit__ tear down the session. A StatusCodeError from connect() (server down, wrong URL, auth rejected) is caught and reported; once the session is open, browseInteractive owns the terminal and any further exceptions bubble out of the with block.

The function returns a string (either a NodeId like "ns=1;i=1001" or a BrowsePath like "/Objects/Plant/Temperature") depending on what the user chose in the quit dialog. The example prints it so the script can be used as a "find me a NodeId" tool from the shell.

try:
    with Client(endpoint_url) as client:
        result = client.browseInteractive(start_nodeid)
        if result is not None:
            print()
            print(f"Selected: {result}")
except StatusCodeError as e:
    print(f"Error: failed to connect: {e.symbol} (0x{e.code:08x})")
    sys.exit(1)

3. Key bindings¶

The browser's input mode is NAV by default; typing / switches to FILTER mode and the keystrokes get a different meaning. The full set of bindings is shown in the browser's built-in ? help screen, but the essentials are:

The "drill into" action opens a modal dialog with three options: return the NodeId, return a BrowsePath, or cancel.

Source Code¶

Download C12_browser.py to run it locally.