Python/ceval.c (part 56)

Source:

cpython 3.14 @ ab2d84fe1023/Python/ceval.c ↗

This annotation covers function object creation and closure capture. See python_ceval55_detail for intrinsic calls and f-string opcodes.

Map

Lines	Symbol	Role
1-80	MAKE_FUNCTION	Create a function object from a code object
81-160	SET_FUNCTION_ATTRIBUTE	Attach defaults, closure, annotations
161-240	COPY_FREE_VARS	Copy closure cells from enclosing frame
241-360	RETURN_CONST	Return a constant (optimized LOAD_CONST + RETURN_VALUE)
361-500	CLEANUP_THROW	Handle exceptions thrown into generators

Reading

MAKE_FUNCTION

// CPython: Python/ceval.c:5620 MAKE_FUNCTION
inst(MAKE_FUNCTION, (codeobj -- func)) {
    PyFunctionObject *func_obj = (PyFunctionObject *)PyFunction_New(codeobj, GLOBALS());
    func = (PyObject *)func_obj;
    DECREF_INPUTS();
    DISPATCH();
}

MAKE_FUNCTION creates a new function from the code object on top of stack and the current globals dict. No defaults or closure are set yet; those come from SET_FUNCTION_ATTRIBUTE.

SET_FUNCTION_ATTRIBUTE

// CPython: Python/ceval.c:5660 SET_FUNCTION_ATTRIBUTE
inst(SET_FUNCTION_ATTRIBUTE, (attr, func -- func)) {
    /* oparg selects which attribute to set:
       MAKE_FUNCTION_DEFAULTS (1): func.__defaults__
       MAKE_FUNCTION_KWDEFAULTS (2): func.__kwdefaults__
       MAKE_FUNCTION_ANNOTATIONS (4): func.__annotations__
       MAKE_FUNCTION_CLOSURE (8): func.__closure__ */
    PyFunctionObject *func_obj = (PyFunctionObject *)func;
    switch (oparg) {
        case MAKE_FUNCTION_DEFAULTS:
            func_obj->func_defaults = Py_NewRef(attr);
            break;
        ...
        case MAKE_FUNCTION_CLOSURE:
            func_obj->func_closure = Py_NewRef(attr);
            break;
    }
    DECREF_INPUTS();
    DISPATCH();
}

The compiler emits SET_FUNCTION_ATTRIBUTE for each optional component. A function with no defaults, no closures, and no annotations only gets MAKE_FUNCTION.

COPY_FREE_VARS

// CPython: Python/ceval.c:5740 COPY_FREE_VARS
inst(COPY_FREE_VARS, (-- )) {
    /* oparg = number of free variables to copy
       At function entry, copy cells from the enclosing frame into the
       current frame's localsplus (the free variable slots) */
    PyCodeObject *co = frame->f_code;
    PyObject *closure = frame->f_func->func_closure;
    int offset = co->co_nlocalsplus - oparg;
    for (int i = 0; i < oparg; i++) {
        PyObject *o = PyTuple_GET_ITEM(closure, i);
        frame->localsplus[offset + i] = Py_NewRef(o);
    }
    DISPATCH();
}

COPY_FREE_VARS runs at function entry for closures. It copies cell references from func.__closure__ into the current frame's free variable slots, making them accessible via LOAD_DEREF.

gopy notes

MAKE_FUNCTION is in vm/eval_simple.go. It calls objects.NewFunction(code, frame.Globals). SET_FUNCTION_ATTRIBUTE sets fields on the objects.Function struct. COPY_FREE_VARS copies from function.Closure (a []*objects.Cell tuple) into frame.Locals[freeVarOffset:].