[Python-ideas] Arguments to exceptions

[Mark E. Haase]

On Thu, Jul 6, 2017 at 5:58 AM, Paul Moore <p.f.moore at gmail.com> wrote:

> To use the (already
>
over-used) NameError example, Ken's proposal doesn't include any
> change to how NameError exceptions are raised to store the name
> separately on the exception.
>

Maybe I'm misunderstanding you, but the proposal has a clear example of
raising NameError and getting the name attribute from the exception
instance:

    try:
        raise NameError(name=name, template="name '{name}' is not defined.")
    except NameError as e:
        name = e.kwargs['name']
        msg = str(e)
        ...

Yes. Because he tries to extract the name component of a NameError,
>
and yet that component isn't stored anywhere - under his proposal or
> under current CPython.
>

I'm not sure what you mean by "extract", but the proposal calls for the
name to be passed as a keyword argument (see above) and stored in
self.kwargs:

    class BaseException:
        def __init__(self, *args, **kwargs):
            self.args = args
            self.kwargs = kwargs

I think this code does what you're asking it to do, right?

(N.B. BaseException is written in C, so this Python code is presumably
illustrative, not an actual implementation.)
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