Propagate exception flag

[MrKevinWeiss]

I would like to know if there is a way that I can propagate an exception instead of catch and print it?

I would expect that this can be some kwarg in the cmd2.__init__ that would allow for the exceptions to be raised instead of printed.

The use case is more for the onecmd functionality. We have a GUI that uses the some built-in commands like run_script and some other custom commands that are only implemented in the cmd2 based application. The exceptions should be caught and displayed by the GUI rather than hidden in the terminal.

Though this can be dealt with on the application level it, maybe I would not be the only one who wants this as an optional argument to be able to control the exceptions?

[kmvanbrunt]

@MrKevinWeiss As you probably saw in onecmd_plus_hooks(), cmd2 already has some custom exception handling for those it doesn't print. As an alternative to adding a parameter to __init__(), we could add a new cmd2 exception class called Cmd2PassthroughException or something similar. You could use this to wrap whatever exception you want. If onecmd_plus_hooks() catches an exception of this type, it will raise it instead of printing it. The question is whether cmd2 should raise the whole Cmd2PassthroughException or just what's wrapped within it.

class Cmd2PassthroughException(Exception):
    """Custom exception class that will be raised instead of printed"""
    def __init__(self, *args, wrapped_ex: BaseException):
        self.wrapped_ex = wrapped_data
        super().__init__(*args)

@tleonhardt @anselor What are your thoughts?

[MrKevinWeiss]

A sound idea, either the whole Cmd2PassthroughException or raising the specific one would work for me. I suppose I have a very slight preference for the specific exception as then the GUI app would not need to import another exception type.

As you probably saw in onecmd_plus_hooks(), cmd2 already has some custom exception handling for those it doesn't print.

No I didn't but that is good to know. 👍

[tleonhardt]

I like the idea of passing that specific exception type through and then unwrapping it and raising the wrapped exception.

[kmvanbrunt]

This is the exception class I added

class PassThroughException(Exception):
    """
    Normally all unhandled exceptions raised during commands get printed to the user.
    This class is used to wrap an exception that should be raised instead of printed.
    """

    def __init__(self, *args, wrapped_ex: BaseException):
        """
        Initializer for PassThroughException
        :param wrapped_ex: the exception that will be raised
        """
        self.wrapped_ex = wrapped_ex
        super().__init__(*args)

[MrKevinWeiss]

Thanks guys!