Objects/methodobject.c (part 4)

Source:

cpython 3.14 @ ab2d84fe1023/Objects/methodobject.c ↗

This annotation covers how C-implemented methods are called. See objects_methodobject3_detail for PyCFunction_NewEx, method slots, and METH_CLASS/METH_STATIC.

Map

Lines	Symbol	Role
1-80	PyCFunction_Call	Dispatch entry point for all C method calls
81-160	METH_VARARGS path	f(self, PyObject *args)
161-240	METH_FASTCALL path	f(self, PyObject *const *, nargs)
241-360	METH_FASTCALL_WITH_KEYWORDS	Add kwnames tuple to fast call
361-500	method_repr	<built-in method name of type object>

Reading

PyCFunction_Call

// CPython: Objects/methodobject.c:88 PyCFunction_Call
PyObject *
PyCFunction_Call(PyObject *func, PyObject *args, PyObject *kwargs)
{
    PyCFunctionObject *f = (PyCFunctionObject *)func;
    int flags = f->m_ml->ml_flags & ~(METH_CLASS | METH_STATIC | METH_COEXIST);
    switch (flags) {
        case METH_VARARGS:
            return (*f->m_ml->ml_meth)(f->m_self, args);
        case METH_VARARGS | METH_KEYWORDS:
            return (*(PyCFunctionWithKeywords)f->m_ml->ml_meth)(f->m_self, args, kwargs);
        case METH_FASTCALL:
            return _PyMethodDef_RawFastCallDict(f->m_ml, f->m_self,
                                                 &PyTuple_GET_ITEM(args, 0),
                                                 PyTuple_GET_SIZE(args), kwargs);
        ...
    }
}

PyCFunction_Call is the legacy entry when args come in as a tuple. For METH_FASTCALL, it bridges the tuple into the C array calling convention. Modern call sites use _PyCFunction_Vectorcall directly.

METH_VARARGS

// CPython: Objects/methodobject.c:140 meth_varargs_call
typedef PyObject *(*PyCFunction)(PyObject *self, PyObject *args);

/* Signature: f(self, args_tuple) */
/* No keyword arguments allowed unless METH_KEYWORDS is also set */

METH_VARARGS is the oldest calling convention. The args tuple is pre-built by the caller. METH_VARARGS | METH_KEYWORDS adds a kwargs dict. Both are fully general but allocate a tuple per call.

METH_FASTCALL

// CPython: Objects/methodobject.c:180 _PyCFunction_Vectorcall
PyObject *
_PyCFunction_Vectorcall(PyObject *func, PyObject *const *stack,
                        size_t nargsf, PyObject *kwnames)
{
    PyCFunctionObject *f = (PyCFunctionObject *)func;
    Py_ssize_t nargs = PyVectorcall_NARGS(nargsf);
    int flags = f->m_ml->ml_flags;
    switch (flags & ~(METH_CLASS | METH_STATIC | METH_COEXIST)) {
        case METH_FASTCALL: {
            if (kwnames != NULL) { ... raise TypeError ... }
            return ((_PyCFunctionFast)f->m_ml->ml_meth)(f->m_self, stack, nargs);
        }
        ...
    }
}

METH_FASTCALL passes arguments as PyObject *const * (a slice of the call stack) with no allocation. This is the preferred convention for new C methods. PyArg_ParseStack unpacks the stack array without a tuple.

METH_FASTCALL_WITH_KEYWORDS

// CPython: Objects/methodobject.c:220 fastcall_keywords
case METH_FASTCALL | METH_KEYWORDS: {
    return ((_PyCFunctionFastWithKeywords)f->m_ml->ml_meth)(
        f->m_self, stack, nargs, kwnames);
}

kwnames is a tuple of keyword argument names; keyword values follow positional values in stack. The callee uses PyArg_ParseStackAndKeywords to unpack both.

method_repr

// CPython: Objects/methodobject.c:340 meth_repr
static PyObject *
meth_repr(PyCFunctionObject *v)
{
    if (v->m_self == NULL || PyModule_Check(v->m_self))
        return PyUnicode_FromFormat("<built-in function %s>",
                                    v->m_ml->ml_name);
    return PyUnicode_FromFormat("<built-in method %s of %s object at %p>",
                                v->m_ml->ml_name,
                                Py_TYPE(v->m_self)->tp_name,
                                v->m_self);
}

Module-level functions display as <built-in function len>. Bound methods display as <built-in method append of list object at 0x...>.

gopy notes

PyCFunction_Call dispatch is in objects/builtin_function.go. METH_VARARGS methods are wrapped as Go func(self Object, args Tuple) Object. METH_FASTCALL methods are func(self Object, args []Object) Object. method_repr is objects.BuiltinFunction.Repr.