[Python-Dev] Is it safe to call PyEval_EvalFrameEx() with an exception set?

[Victor Stinner]

2013/7/16 Antoine Pitrou <solipsis at pitrou.net>:
> Le Tue, 16 Jul 2013 02:34:49 +0200,
> Victor Stinner <victor.stinner at gmail.com> a écrit :
>> I would like to add assertions in Python/ceval.c to detect such bugs
>> earlier. The problem is that some functions rely on the ability to
>> call PyEval_EvalFrameEx() with an exception set. Is it expected?
>> Should it be avoided?
>
> Well, if your frame is a generator frame, you must be able to throw()
> into it, i.e. resume it with an exception set.
>
> The difficulty here is that there are different meanings for "an
> exception is set":
> - PyErr_Occurred() is true
> - the f_exc_type field and friends are set
> - possibly another one that I'm forgetting about

Ah yes, a generator can call PyEval_EvalFrameEx() with an exception
set (PyErr_Occurred() is non-NULL), but it sets throwflag to 1.

My question is when an exception is set (PyErr_Occurred() is non-NULL)
at the beginning of the bytecode evaluation loop. Just after the "goto
error;" in this extract of ceval.c:

    if (throwflag) /* support for generator.throw() */
        goto error;

    for (;;) { ... }

Victor