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bpo-46841: Don't jump during throw() #31968

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6ee3f38
Handle return-during-throw in SEND
brandtbucher Mar 17, 2022
dcf97b2
Update the docs for SEND
brandtbucher Mar 17, 2022
fb649c7
blurb add
brandtbucher Mar 17, 2022
acdf984
Clean things up a bit
brandtbucher Mar 17, 2022
4d30025
Catch up with main
brandtbucher Apr 6, 2022
f3d7fbe
Catch up with main
brandtbucher May 6, 2022
67a63b2
Catch up with main
brandtbucher Jun 8, 2022
5aebc87
Minor doc edits
brandtbucher Jun 8, 2022
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16 changes: 13 additions & 3 deletions Doc/library/dis.rst
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Expand Up @@ -1313,13 +1313,23 @@ iterations of the loop.
.. versionadded:: 3.11


.. opcode:: SEND
.. opcode:: SEND (delta)

Sends ``None`` to the sub-generator of this generator.
Used in ``yield from`` and ``await`` statements.
Equivalent to ``TOS = TOS1.send(TOS)``. Used in ``yield from`` and ``await``
statements.

If the call raises :exc:`StopIteration`, pop both values, push its return
value, and increment the bytecode counter by *delta*.

If TOS1 is ``NULL`` (set when a ``throw()`` through the current frame
returns), pop both values, push TOS (its return value) back, and increment
the bytecode counter by *delta*.

.. versionadded:: 3.11

.. versionchanged:: 3.12
Added ``NULL`` handling for subiterators that return during ``throw()``.


.. opcode:: ASYNC_GEN_WRAP

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2022-03-17-11-40-20.bpo-46841.cU7e6B.rst
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@@ -0,0 +1,3 @@
When a sub-iterator returns a value during a ``throw()`` call, perform the
resulting jump during the next :opcode:`SEND` instruction (rather than as
part of the ``throw()`` implementation).
10 changes: 2 additions & 8 deletions Objects/genobject.c
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Expand Up @@ -491,14 +491,8 @@ _gen_throw(PyGenObject *gen, int close_on_genexit,
ret = _PyFrame_StackPop((_PyInterpreterFrame *)gen->gi_iframe);
assert(ret == yf);
Py_DECREF(ret);
// XXX: Performing this jump ourselves is awkward and problematic.
// See https://github.com/python/cpython/pull/31968.
/* Termination repetition of SEND loop */
assert(_PyInterpreterFrame_LASTI(frame) >= 0);
/* Backup to SEND */
assert(_Py_OPCODE(frame->prev_instr[-1]) == SEND);
int jump = _Py_OPARG(frame->prev_instr[-1]);
frame->prev_instr += jump - 1;
// NULL tells SEND to quit sending:
_PyFrame_StackPush((_PyInterpreterFrame *)gen->gi_iframe, NULL);
if (_PyGen_FetchStopIterationValue(&val) == 0) {
ret = gen_send(gen, val);
Py_DECREF(val);
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6 changes: 6 additions & 0 deletions Python/ceval.c
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Expand Up @@ -2591,6 +2591,12 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
assert(STACK_LEVEL() >= 2);
PyObject *v = POP();
PyObject *receiver = TOP();
if (receiver == NULL) {
// Receiver returned during a throw(). v is its return value:
SET_TOP(v);
JUMPBY(oparg);
DISPATCH();
}
PySendResult gen_status;
PyObject *retval;
if (tstate->c_tracefunc == NULL) {
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