[Python-Dev] NULL allowed in PyErr_SetString and friends?

Eli Bendersky eliben at gmail.com
Mon Aug 12 15:01:57 CEST 2013

On Mon, Aug 12, 2013 at 5:10 AM, Antoine Pitrou <solipsis at pitrou.net> wrote:

> Hello,
> It seems NULL is allowed as the first argument of PyErr_Format,
> PyErr_SetString and PyErr_SetObject. Moreover, it means "clear the
> error indicator". However, this is not mentioned in the docs. I was
> wondering if we should officialize this behaviour or change it.

Since the same capability is available much more clearly through
PyError_Clear (and also through PyError_Restore(NULL, NULL, NULL)), IMHO we
should at least:

1. Document that NULL is not allowed in PyErr_Set{Object|String}
2. Switch all actual uses of that idiom in the stdlib to PyError_Clear

If we don't fear external code breakaga that relies on this undocumented
behavior, we can also add explicit treating of NULL in
PyErr_Set{Object|String} (maybe even asserting). Otherwise, we can just
keep the behavior as is for now, though make it more correct: to do the
reset it would call PyError_Restore(NULL, value, tb) even though
PyError_Restore documents that all args should be NULL to actually clear
the indicator.

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