Python/ceval.c (part 11)

Source:

cpython 3.14 @ ab2d84fe1023/Python/ceval.c

This annotation covers iterator and generator opcodes. See python_ceval10_detail for CALL specializations and python_ceval_detail for the main eval loop.

Map

Lines	Symbol	Role
1-100	`FOR_ITER_LIST`	`for x in list` — direct list iteration
101-200	`FOR_ITER_TUPLE`	`for x in tuple` — direct tuple iteration
201-300	`FOR_ITER_RANGE`	`for x in range(n)` — counter-based iteration
301-400	`FOR_ITER_GEN`	`for x in gen` — inline generator advance
401-550	`SEND`	Send a value into a generator or coroutine (`gen.send(val)`)
551-650	`YIELD_VALUE`	Suspend the current generator frame
651-800	`GET_AITER` / `GET_ANEXT`	Async iteration: `async for` desugaring

Reading

`FOR_ITER_LIST`

// CPython: Python/ceval.c:5280 FOR_ITER_LIST
inst(FOR_ITER_LIST, (unused/1, iter -- iter, next)) {
    DEOPT_IF(Py_TYPE(iter) != &PyListIter_Type, FOR_ITER);
    PyListIterObject *it = (PyListIterObject *)iter;
    PyListObject *seq = it->it_seq;
    DEOPT_IF(seq == NULL, FOR_ITER);
    DEOPT_IF(it->it_index >= PyList_GET_SIZE(seq), FOR_ITER);
    next = PyList_GET_ITEM(seq, it->it_index);
    Py_INCREF(next);
    it->it_index++;
    DECREMENT_ADAPTIVE_COUNTER(this_instr[-1].cache);
}

Avoids the tp_iternext virtual call for list iterators.

`FOR_ITER_RANGE`

// CPython: Python/ceval.c:5400 FOR_ITER_RANGE
inst(FOR_ITER_RANGE, (unused/1, iter -- iter, next)) {
    DEOPT_IF(Py_TYPE(iter) != &PyRangeIter_Type, FOR_ITER);
    PyRangeIterObject *r = (PyRangeIterObject *)iter;
    DEOPT_IF(r->len == 0, FOR_ITER);  /* exhausted */
    long value = r->start;
    r->start = value + r->step;
    r->len--;
    next = PyLong_FromLong(value);  /* or use compact int cache */
    DECREMENT_ADAPTIVE_COUNTER(this_instr[-1].cache);
}

For range(1000), no Python int objects are created if values fit in the small-int cache.

`SEND`

// CPython: Python/ceval.c:5620 SEND
inst(SEND, (unused/1, receiver, v -- receiver, retval)) {
    /* receiver.send(v) — used in 'yield from' and 'await' */
    if (tstate->c_tracefunc == NULL) {
        if (PyGen_CheckExact(receiver) || PyCoro_CheckExact(receiver)) {
            /* Inline: push new frame for the generator */
            retval = gen_send_ex((PyGenObject *)receiver, v, 0, 0);
        }
    }
    ...
}

SEND is the opcode generated for yield from and await. It sends a value to the sub-generator without an extra Python call.

`YIELD_VALUE`

// CPython: Python/ceval.c:5780 YIELD_VALUE
inst(YIELD_VALUE, (retval -- retval)) {
    /* Suspend the current generator frame */
    frame->gi_frame_state = FRAME_SUSPENDED;
    _PyFrame_SetStackPointer(frame, stack_pointer - 1);
    /* Return retval to the caller of send()/next() */
    DISPATCH_TO_CALLER();
}

After YIELD_VALUE, the frame's prev_instr points past the YIELD instruction. The next send() call resumes from there.

`GET_AITER` / `GET_ANEXT`

// CPython: Python/ceval.c:5900 GET_AITER
inst(GET_AITER, (obj -- aiter)) {
    /* aiter = type(obj).__aiter__(obj) */
    unaryfunc tp_aiter = Py_TYPE(obj)->tp_as_async->am_aiter;
    if (tp_aiter == NULL)
        _PyErr_Format(tstate, PyExc_TypeError,
            "'async for' requires an object with __aiter__ method, got %.100s",
            Py_TYPE(obj)->tp_name);
    aiter = (*tp_aiter)(obj);
}

async for x in aobj desugars to: GET_AITER, then a loop of GET_ANEXT + SEND (to drive the coroutine) + STORE_FAST.

gopy notes

FOR_ITER_LIST, FOR_ITER_RANGE are specialized in vm/eval_specialize.go. SEND drives generators via objects.GenSendEx in objects/genobject.go. YIELD_VALUE sets frame.FrameState = FrameSuspended and returns to the caller frame. GET_AITER/GET_ANEXT use objects.GetAIter/GetANext.

Map​

Reading​

FOR_ITER_LIST​

FOR_ITER_RANGE​

SEND​

YIELD_VALUE​

GET_AITER / GET_ANEXT​

gopy notes​

Map