Objects/classobject.c (part 2)

cpython 3.14 @ ab2d84fe1023/Objects/classobject.c ↗

This annotation covers the method call path, vectorcall support, and pickling in Objects/classobject.c. For the basic PyMethodObject struct and __get__ descriptor see the objects_method annotation.

Map

Lines	Symbol	Role
1-80	PyMethod_New	Bound method construction
81-200	method_call, method_vectorcall	Dispatching a method call
201-320	method_reduce	Pickling support
321-420	PyMethod_GET_FUNCTION, PyMethod_GET_SELF	Inline accessors

Reading

method_vectorcall

When the function stored in a bound method implements the vectorcall protocol, method_vectorcall avoids building an argument tuple. It prepends self to the argument vector using the PY_VECTORCALL_ARGUMENTS_OFFSET trick (borrows one slot before the array pointer).

// CPython: Objects/classobject.c:110 method_vectorcall
static PyObject *
method_vectorcall(PyObject *method, PyObject *const *args,
                  size_t nargsf, PyObject *kwnames)
{
    PyObject *self = PyMethod_GET_SELF(method);
    PyObject *func = PyMethod_GET_FUNCTION(method);
    Py_ssize_t nargs = PyVectorcall_NARGS(nargsf);
    /* Prepend self by moving the pointer back one slot */
    PyObject *const *newargs = args - 1;
    newargs[0] = self;
    return func->ob_type->tp_vectorcall(func, newargs, nargs + 1, kwnames);
}

Pickling

method_reduce returns (getattr, (self, method_name)) so that unpickling a bound method calls getattr(self, name) to reconstruct it. This only works for methods that can be looked up by name.

Unbound call type check

When a function is called with an explicit first argument that is not an instance of the expected type (a pre-Python-3 pattern), CPython 3 raises TypeError explaining that the descriptor expected a specific type.

gopy notes

objects/method.go implements PyMethodObject. The vectorcall path (method_vectorcall) is not yet implemented; all calls go through __call__. The PY_VECTORCALL_ARGUMENTS_OFFSET slot trick is specific to the CPython memory layout and has no direct Go equivalent.