$ ./python 
Python 3.2rc1+ (unknown, Jan 18 2011, 00:55:20) 
>>> import _string
>>> _string.formatter_field_name_split(1)
python: Objects/stringlib/string_format.h:1347: formatter_field_name_split: Assertion `((((((PyObject*)(self))->ob_type))->tp_flags & ((1L<<28))) != 0)' failed.
Abandon

$ ./python 
Python 3.2rc1+ (unknown, Jan 18 2011, 00:55:20) 
>>> import _string
>>> _string.formatter_parser(1)
python: Objects/stringlib/string_format.h:1206: formatter_parser: Assertion `((((((PyObject*)(self))->ob_type))->tp_flags & ((1L<<28))) != 0)' failed.
Abandon

Attached patch fixes both crashes and add tests on the _string module (which has only these two functions).

I'll review this tomorrow.

The patch looks good to me. I've added some more tests to cover some corner cases.

Go ahead and commit it.

Release manager: You can decide if this fix should go in before 3.2. It's a trivial fix to a crasher, but it's extremely unlikely anyone would trip over it. It's been a crasher since 3.0.

It's also a crasher in 2.7, although there it's in the str module and the method names have leading underscores.

2011/1/28 Eric Smith <report@bugs.python.org>:
>
> Eric Smith <eric@trueblade.com> added the comment:
>
> Release manager: You can decide if this fix should go in before 3.2. It's a trivial fix to a crasher, but it's extremely unlikely anyone would trip over it. It's been a crasher since 3.0.

Fine w/ me.

>
> It's also a crasher in 2.7, although there it's in the str module and the method names have leading underscores.
>
> ----------
> assignee:  -> georg.brandl
> components: +Extension Modules -Library (Lib)
> nosy: +benjamin.peterson, georg.brandl
> priority: normal -> release blocker
> title: _string: formatter_field_name_split() and formatter_parser doesn't check input type -> _string: formatter_field_name_split() and formatter_parser() don't check input type
> versions: +Python 2.7
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue11032>
> _______________________________________
>

I think the canonical message is "expected X, not Y".  Otherwise, fine to commit.

It looks like the canonical message is "expected X, got Y". With that change I've checked it in in r88226. I'll backport.

Actually this error doesn't exist on older versions because these used to be methods on a string. The error was introduced in r85456 (issue 9418) when these became functions in the _string module.

No need to backport.