Objects/abstract.c (part 4)

Source:

cpython 3.14 @ ab2d84fe1023/Objects/abstract.c ↗

This annotation covers iteration and calling protocol. See objects_abstractobject3_detail for PyNumber_*, PySequence_*, and PyMapping_*.

Map

Lines	Symbol	Role
1-80	PyObject_GetIter	Get an iterator from any iterable
81-160	PyIter_Next	Advance an iterator
161-260	PyObject_Call	Call with args+kwargs tuple/dict
261-360	PyObject_Vectorcall	Call with C array + kwnames
361-500	PyObject_CallOneArg / _NoArgs	Convenience callers

Reading

PyObject_GetIter

// CPython: Objects/abstract.c:2780 PyObject_GetIter
PyObject *
PyObject_GetIter(PyObject *o)
{
    PyTypeObject *t = Py_TYPE(o);
    getiterfunc f;
    f = t->tp_iter;
    if (f == NULL) {
        /* Fall back: if tp_as_sequence->sq_item is defined, wrap in a sequence iterator */
        if (t->tp_as_sequence && t->tp_as_sequence->sq_item) {
            return PySeqIter_New(o);
        }
        PyErr_Format(PyExc_TypeError, "'%.200s' object is not iterable", t->tp_name);
        return NULL;
    }
    PyObject *res = (*f)(o);
    ...
    return res;
}

iter(obj) calls tp_iter. If not defined but sq_item is, a seqiterobject wraps the object, calling sq_item(obj, 0), sq_item(obj, 1), etc. until IndexError.

PyObject_Vectorcall

// CPython: Objects/abstract.c:2920 PyObject_Vectorcall
PyObject *
PyObject_Vectorcall(PyObject *callable, PyObject *const *args,
                    size_t nargsf, PyObject *kwnames)
{
    /* nargsf encodes nargs in the lower bits;
       PY_VECTORCALL_ARGUMENTS_OFFSET is set if args[-1] can be overwritten */
    assert(nargs >= 0);
    vectorcallfunc func = _PyVectorcall_Function(callable);
    if (func == NULL) {
        return _PyObject_MakeTpCall(NULL, callable, args, nargs, kwnames);
    }
    return func(callable, args, nargsf, kwnames);
}

Vectorcall is the fast calling convention added in PEP 590. Instead of building a tuple of arguments, callers pass a C array directly. Functions expose tp_vectorcall_offset pointing to their vectorcall function pointer.

PyObject_CallOneArg

// CPython: Objects/abstract.c:2980 PyObject_CallOneArg
PyObject *
PyObject_CallOneArg(PyObject *func, PyObject *arg)
{
    assert(arg != NULL);
    PyObject *const args[1] = {arg};
    return PyObject_Vectorcall(func, args, 1 | PY_VECTORCALL_ARGUMENTS_OFFSET, NULL);
}

PyObject_CallOneArg is a vectorcall wrapper for single-argument calls. PY_VECTORCALL_ARGUMENTS_OFFSET signals that args[-1] is a valid slot the callee can use temporarily.

gopy notes

PyObject_GetIter is objects.GetIter in objects/abstract.go. It checks for objects.IterableProtocol first (Go interface), then falls back to sequence wrapping. PyObject_Vectorcall is objects.Vectorcall, which passes a Go slice directly to avoid intermediate allocations. PyObject_CallOneArg calls objects.CallOneArg.