Include/cpython/funcobject.h — function object internals

CPython stores every Python def statement as a PyFunctionObject. This header exposes the full C layout used by the interpreter, the accessor macros that the eval loop calls on every CALL opcode, the PyCFunction family of typedefs for built-in callables, and the PyMethodDef table that wires C functions into module or type method lists.

Map

Lines	Symbol	Kind	Notes
1-10	guard + includes	boilerplate	depends on funcobject.h (public)
12-35	PyFunctionObject	struct	full field layout, see Reading below
37-42	PyFunction_GET_CODE	macro	reads func_code without incref
43-48	PyFunction_GET_GLOBALS	macro	reads func_globals without incref
49-54	PyFunction_GET_CLOSURE	macro	reads func_closure, may be NULL
56-70	PyCFunction / PyCFunctionWithKeywords	typedef	C-level call signatures
72-90	PyMethodDef	struct	name, meth pointer, flags, doc
92-110	CO_OPTIMIZED and friends	#define	code-object flag bits
112-120	PyFunction_NewWithQualName	C API	internal constructor

Reading

PyFunctionObject layout

The struct holds every attribute visible on a Python function object. Key fields:

typedef struct {
    PyObject_HEAD
    PyObject *func_code;       /* PyCodeObject — the bytecode */
    PyObject *func_globals;    /* dict — the defining module's globals */
    PyObject *func_defaults;   /* tuple or NULL */
    PyObject *func_kwdefaults; /* dict or NULL */
    PyObject *func_closure;    /* tuple of cells or NULL */
    PyObject *func_doc;
    PyObject *func_name;
    PyObject *func_dict;
    PyObject *func_weakreflist;
    PyObject *func_module;
    PyObject *func_annotations;
    PyObject *func_typeparams;
    vectorcallfunc vectorcall;
} PyFunctionObject;

func_closure is a tuple of PyCellObject values. The closure is NULL for functions that capture no free variables, so callers must guard before indexing.

Accessor macros

The three GET macros return borrowed references and skip the type check that PyObject_GetAttr would perform, making them safe only inside the eval loop where the type is already guaranteed.

#define PyFunction_GET_CODE(func)    (((PyFunctionObject *)func)->func_code)
#define PyFunction_GET_GLOBALS(func) (((PyFunctionObject *)func)->func_globals)
#define PyFunction_GET_CLOSURE(func) (((PyFunctionObject *)func)->func_closure)

PyCFunction typedefs and PyMethodDef

Built-in functions exposed to Python are typed as one of:

typedef PyObject *(*PyCFunction)(PyObject *self, PyObject *args);
typedef PyObject *(*PyCFunctionWithKeywords)(PyObject *self,
                                             PyObject *args,
                                             PyObject *kwargs);

PyMethodDef binds a name string to one of these pointers, a flags word (METH_VARARGS, METH_FASTCALL, METH_NOARGS, etc.), and an optional doc string. A NULL-terminated array of PyMethodDef is what PyModule_Create iterates to populate a module's namespace.

gopy notes

• objects/function.go mirrors PyFunctionObject as Function with the same field set. FuncCode, FuncGlobals, and FuncClosure map one-for-one.
• The GET macros correspond to Go methods Code(), Globals(), and Closure() on *Function; all return unretained pointers matching the borrowed-ref semantics of the macros.
• PyMethodDef is represented as objects.MethodDef; module initialization iterates the slice in objects/module.go the same way CPython's PyModule_Create iterates the C array.
• CO_* flag bits are declared in compile/compiler.go as typed constants and checked during code-object construction.