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Re: except clause syntax question

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On Tue, Jan 31, 2012 at 6:09 PM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
> On Tue, Jan 31, 2012 at 5:53 PM, Chris Angelico <rosuav@gmail.com> wrote:
>> On Wed, Feb 1, 2012 at 9:03 AM, Duncan Booth
>> <duncan.booth@invalid.invalid> wrote:
>>> Abitrarily nested tuples of exceptions cannot contain loops so the code
>>> simply needs to walk through the tuples until it finds a match.
>>
>> Is this absolutely guaranteed? The C API for CPython provides:
>> (Py2) http://docs.python.org/c-api/tuple.html#PyTuple_SetItem
>> (Py3) http://docs.python.org/dev/c-api/tuple.html#PyTuple_SetItem
>>
>> which doesn't have massive warnings on it saying "USE THIS ONLY TO
>> INITIALIZE A TUPLE" (compare, for instance, _PyTuple_Resize which does
>> carry a similar warning). Is the assumption then that we're all
>> adults, and that mutating a tuple is like passing a null pointer to an
>> API function (aka "loaded gun in proximity to foot")?
>
> I don't know why the docs are written the way that they are, but if
> you check the code, you can see that PyTuple_SetItem will raise a
> SystemError if the reference count is anything other than 1.  So I
> think that it is only meant to be used with similar caution and
> restraint.

Incidentally, I *think* that any correctly written C code attempting
to nest a tuple inside itself would make the reference count of the
tuple be at least 2 at the time of the call, and so it would fail.

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except clause syntax question Charles Yeomans <charles@declareSub.com> - 2012-01-30 12:41 -0500
  Re: except clause syntax question Mel Wilson <mwilson@the-wire.com> - 2012-01-30 14:15 -0500
  Re: except clause syntax question Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-01-31 00:00 +0000
    Re: except clause syntax question Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-01-30 19:25 -0500
    Re: except clause syntax question Charles Yeomans <charles@declareSub.com> - 2012-01-31 08:57 -0500
      Re: except clause syntax question Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-01-31 14:51 +0000
        Re: except clause syntax question Charles Yeomans <charles@declareSub.com> - 2012-01-31 11:23 -0500
        Re: except clause syntax question Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-01-31 11:38 -0500
        Re: except clause syntax question Charles Yeomans <charles@declaresub.com> - 2012-01-31 12:29 -0500
        Re: except clause syntax question Ethan Furman <ethan@stoneleaf.us> - 2012-01-31 08:56 -0800
    Re: except clause syntax question Terry Reedy <tjreedy@udel.edu> - 2012-01-31 19:12 -0500
    Re: except clause syntax question Charles Yeomans <charles@declareSub.com> - 2012-01-31 19:27 -0500
  Re: except clause syntax question Mel Wilson <mwilson@the-wire.com> - 2012-01-31 08:24 -0500
    Re: except clause syntax question Charles Yeomans <charles@declareSub.com> - 2012-01-31 13:04 -0500
  Re: except clause syntax question Duncan Booth <duncan.booth@invalid.invalid> - 2012-01-31 22:03 +0000
    Re: except clause syntax question Chris Angelico <rosuav@gmail.com> - 2012-02-01 11:53 +1100
      Re: except clause syntax question Mel Wilson <mwilson@the-wire.com> - 2012-01-31 23:39 -0500
    Re: except clause syntax question Ian Kelly <ian.g.kelly@gmail.com> - 2012-01-31 18:09 -0700
    Re: except clause syntax question Ian Kelly <ian.g.kelly@gmail.com> - 2012-01-31 18:12 -0700
    Re: except clause syntax question Chris Angelico <rosuav@gmail.com> - 2012-02-01 13:46 +1100

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