[Python-3000] Pre-peps on raise and except changes

[Brett Cannon]

On 1/23/07, Collin Winter <collinw at gmail.com> wrote:
> On 1/23/07, Nick Coghlan <ncoghlan at gmail.com> wrote:
> > Phillip J. Eby wrote:
> > > The 2-expression "raise" statement translation is incorrect in the general
> > > case; it is possible for the second argument to be an instance of the first
> > > argument, in which case 'raise E, V' should become just 'raise V'.  This is
> > > not detectable by the refactoring tool, AFAIK.
> >
> > There is another issue which currently isn't entirely clear in this PEP
> > or in PEP 352 - what happens to except statements which raise a subtype
> > of Exception instead of an instance of it.
> >
> > It's currently implicit that this will continue to be allowed (with
> > subtypes being automatically instantiated with no arguments) - I think
> > that behaviour should be explicitly stated as intentional in the new
> > Py3k PEP.
>
> Does this language work for you?
>
> """
> 2. ``raise E`` (with a single argument) is used to raise a new
>    exception.

For some reason I thought you were initially talking about a single
argument to the exception, not to E.

>This form has two sub-variants: ``E`` may be either an
>    instance of ``BaseException`` [#pep352]_ or a subclass of
>    ``BaseException``. If ``E`` is a subclass, it will be called with
>    no arguments to obtain an exception instance.
>
>    To raise anything else is an error.
> """

I don't think that calling them a variant is right.  You can only
raise subclasses of BaseException (which implicitly implies
BaseException itself).  If you want to mention BaseException itself
that's fine, but there is no variant here; there is a single rule.

-Brett