[Python-Dev] RE: test_sort.py failure

Armin Rigo arigo at tunes.org
Thu Jul 29 11:33:55 CEST 2004

Hello Tim,

On Thu, Jul 29, 2004 at 12:11:31AM -0400, Tim Peters wrote:
> It's checked in now.

Unfortunately it is not true that ob_item can never be set to NULL with normal
list operations.  list_ass_slice() and list_inplace_repeat() can both do that.  
The former is not so rare as it is used e.g. for 'del lst[:]'.

The invariants of the ob_xxx list members should be clearly specified
somewhere and we should stick to them.  E.g. it is unclear to me why we allow
list_ass_slice() to reset ob_item to NULL and ob_size to 0 without resetting
ob_allocated to 0 -- I see why it doesn't crash in a subsequent list_resize(),
but it looks messy.

Alternatively, the quickest fix for the broken listsort() would have been to
keep the empty_ob_item hack but just check that ob_allocated is still zero in
addition to ob_size.  However the current version is quite clean and can be
made bulletproof by ensuring that ob_item is never reset to NULL.

A bientot,


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