Objects/methodobject.c

Source:

cpython 3.14 @ ab2d84fe1023/Objects/methodobject.c

Objects/methodobject.c implements PyCFunctionObject and PyCMethodObject, which wrap C function pointers as callable Python objects. Every built-in function (len, print, range) and every method defined via PyMethodDef uses one of these types.

Map

Lines	Symbol	Role
1-80	`PyCFunction_NewEx`, `PyCMethod_New`	Constructors
81-200	`PyCFunction_Call`, `method_call`	Calling conventions dispatch
201-350	`PyCFunction_GET_FUNCTION`, `PyCFunction_GET_FLAGS`	Accessor macros
351-500	`tp_repr`, `tp_richcompare`, `tp_hash`	Slots for built-in function type
501-600	`PyMethodDef` registration, `PyCFunctionObject` type def	Type object

Reading

Calling conventions

PyMethodDef.ml_flags selects the calling convention:

Flag	Signature	Notes
`METH_VARARGS`	`f(self, args)`	Classic; `args` is a tuple
`METH_VARARGS	METH_KEYWORDS`	`f(self, args, kwargs)`
`METH_FASTCALL`	`f(self, *args, nargs)`	C array of PyObject*
`METH_FASTCALL	METH_KEYWORDS`	`f(self, *args, nargs, kwnames)`
`METH_NOARGS`	`f(self, NULL)`	No arguments
`METH_O`	`f(self, arg)`	Exactly one argument
`METH_CLASS`	prepended	`classmethod` variant
`METH_STATIC`	prepended	`staticmethod` variant

`method_call` dispatch

// CPython: Objects/methodobject.c:140 method_call
static PyObject *
method_call(PyObject *func, PyObject *args, PyObject *kwargs)
{
    PyCFunction meth = PyCFunction_GET_FUNCTION(func);
    PyObject *self = PyCFunction_GET_SELF(func);
    int flags = PyCFunction_GET_FLAGS(func);

    switch (flags & ~(METH_CLASS | METH_STATIC | METH_COEXIST)) {
    case METH_VARARGS:
        ...
        return meth(self, args);
    case METH_VARARGS | METH_KEYWORDS:
        return ((PyCFunctionWithKeywords)(void(*)(void))meth)(self, args, kwargs);
    case METH_FASTCALL | METH_KEYWORDS:
        return _PyCFunction_Vectorcall(func, ...);
    ...
    }
}

`PyCMethod_New` and the `module` attribute

PyCMethod_New creates a method bound to a specific type (cls), used for METH_CLASS methods. The type is stored in m_ml (the PyMethodDef) and accessible as __self__.__class__.

Vectorcall support

PyCFunctionObject implements the vectorcall protocol (tp_vectorcall). This allows the interpreter to call built-in functions via CALL_INTRINSIC_1 and CALL_BUILTIN_FAST specialized opcodes without creating an intermediate tuple.

gopy notes

The gopy equivalent is objects/method.go. Built-in methods are Go functions wrapped in a Method struct that holds the function pointer and calling convention flags. The vectorcall fast path is approximated by direct Go function calls when the call site is monomorphic.

Map​

Reading​

Calling conventions​

method_call dispatch​

PyCMethod_New and the __module__ attribute​

Vectorcall support​

gopy notes​

Map