Returning Python exceptions to LabVIEW

[Phillip Brooks]

I am writing a wrapper to a Python class.

The class has several states and will raise an exception when a method is called that is incompatible with the current state.

Are there any best practices for passing exceptions back to LabVIEW? I was thinking of using the LabVIEW error cluster as a return type.

[bbean]

On 4/5/2022 at 8:56 AM, Phillip Brooks said:

I am writing a wrapper to a Python class.

The class has several states and will raise an exception when a method is called that is incompatible with the current state.

Are there any best practices for passing exceptions back to LabVIEW? I was thinking of using the LabVIEW error cluster as a return type.

That seems reasonable.  I have a wrapper class and pass back a pass/fail numeric and a status string,  but now thinking back it might have been more appropriate to just pass back a standard labview error cluster.

In my case, the python wrapper can be run from either LabVIEW or directly in python.  The thing i struggle with is passing back real-time status that normally is provided in the terminal via python print statements when python scripts run stand-alone.  I'm testing an approach that just sends these via a UDP session but I haven't found a way to override the Python print command so that it prints to both the terminal (python scripts) and to the UDP session (LabVIEW VIs).

[Stagg54]

55 minutes ago, bbean said:

I haven't found a way to override the Python print command so that it prints to both the terminal (python scripts) and to the UDP session (LabVIEW VIs).

I'm no Python guru,

but maybe a decorator?

and or maybe monkeypatching?

or some combination?

[Phillip Brooks]

The creator of the class had provided an example code module that included functions with a return value tuple of (bool, str) representing function call success and optional string.

I was conflating this return value in the example with an error. We modified the wrapper code module functions to raise an exception. 

I learned that the LabVIEW Python Node 'error out' connector handles a Python raise exception by returning an error with a code of 1671 and source string that contains the exception message ( is this documented somewhere? )

This is very nice! Now if we call a function where the Python object is in the wrong state, we get a LabVIEW error 1671 and the class exception string within the error out source (.e.g. "Failure to add measurement; test_run_state = [IDLE]").