Objects/funcobject.c

Source:

cpython 3.14 @ ab2d84fe1023/Objects/funcobject.c ↗

Map

Lines	Symbol	What it does
1-50	struct PyFunctionObject	Struct layout: func_code, func_globals, func_defaults, func_closure, etc.
51-120	PyFunction_New	Allocates a new function object from a code object and globals dict
121-180	PyFunction_NewWithQualName	Variant that also sets qualname at construction time
181-250	func_doc get/set	doc descriptor: reads and writes func_doc field
251-310	func_name get/set	name descriptor: validates string type, updates func_name
311-370	func_qualname get/set	qualname descriptor: validates string type, updates func_qualname
371-440	func_defaults get/set	defaults descriptor: validates tuple or None, updates func_defaults
441-510	func_kwdefaults get/set	kwdefaults descriptor: validates dict or None, updates func_kwdefaults
511-580	func_annotations get/set	annotations descriptor: lazy dict creation, updates func_annotations
581-650	func_closure get/set	closure descriptor: read-only tuple of cell objects
651-720	func_call	tp_call slot: extracts defaults and closure, dispatches to _PyEval_EvalCodeWithName
721-800	PyFunction_Type	Type object definition with all slots wired

Reading

PyFunctionObject layout

Every Python def statement produces a PyFunctionObject. The struct carries the compiled code object plus everything the runtime needs to call it: the global namespace, default argument values, keyword-only defaults, annotations, and the closure tuple.

// CPython: Objects/funcobject.c:20 PyFunctionObject
typedef struct {
    PyObject_HEAD
    PyObject *func_code;       /* A code object, the __code__ attribute */
    PyObject *func_globals;    /* A dictionary (the __globals__ attribute) */
    PyObject *func_defaults;   /* NULL or a tuple */
    PyObject *func_kwdefaults; /* NULL or a dict */
    PyObject *func_closure;    /* NULL or a tuple of cell objects */
    PyObject *func_doc;
    PyObject *func_name;
    PyObject *func_dict;
    PyObject *func_weakreflist;
    PyObject *func_module;
    PyObject *func_annotations;
    PyObject *func_qualname;
    vectorcallfunc vectorcall;
} PyFunctionObject;

The func_closure field is a tuple of PyCellObject items, one per free variable in func_code->co_freevars. The compiler ensures the lengths always match at call time.

PyFunction_New and construction

PyFunction_New is called by the MAKE_FUNCTION bytecode instruction. It receives a code object and the current frame's f_globals dict. The qualname variant is used when the compiler knows the qualified name at compile time (class methods, nested functions).

// CPython: Objects/funcobject.c:63 PyFunction_New
PyObject *
PyFunction_New(PyObject *code, PyObject *globals)
{
    return PyFunction_NewWithQualName(code, globals, NULL);
}

After the allocation, PyFunction_NewWithQualName copies co_name into func_name and either the supplied qualname or co_qualname into func_qualname. Both func_defaults and func_closure start as NULL; they are filled in by subsequent SET_FUNCTION_ATTRIBUTE instructions emitted by the compiler.

Attribute descriptors and func_call

The get/set descriptors (func_doc, func_name, func_qualname, func_defaults, func_kwdefaults, func_annotations) follow the same shape: the getter returns the stored field (or None/empty-dict for annotations), and the setter type-checks the incoming value before storing it. Storing None to func_defaults clears the field to NULL.

// CPython: Objects/funcobject.c:375 func_defaults_set
static int
func_defaults_set(PyFunctionObject *op, PyObject *value, void *Py_UNUSED(ignored))
{
    if (value == Py_None)
        value = NULL;
    if (value != NULL && !PyTuple_Check(value)) {
        PyErr_SetString(PyExc_TypeError,
                        "__defaults__ must be set to a tuple object");
        return -1;
    }
    Py_XSETREF(op->func_defaults, Py_XNewRef(value));
    return 0;
}

func_call (the tp_call slot) is a thin wrapper. It unpacks func_defaults and func_kwdefaults from the struct and forwards to _PyEval_EvalCodeWithName, which sets up the frame.

gopy notes

Status: not yet ported.

Planned package path: objects/ as objects/function.go (struct) and objects/function_attrs.go (descriptors).

The PyFunctionObject struct maps directly onto the existing FunctionObject type in objects/function.go. The descriptor logic for __defaults__ and __kwdefaults__ is needed for keyword argument support in the VM. The func_closure get/set pair is required before any closure-bearing function can be called correctly. func_call itself is superseded by the vectorcall path in gopy's VM, but the attribute accessors are all needed.