Python虚拟机函数机制之闭包和装饰器（七）

>>> def f(a, b):
...     c = a + b
...     print(c)
... 
>>> import dis
>>> dis.dis(f)
  2           0 LOAD_FAST                0 (a)
              3 LOAD_FAST                1 (b)
              6 BINARY_ADD          
              7 STORE_FAST               2 (c)

  3          10 LOAD_FAST                2 (c)
             13 PRINT_ITEM          
             14 PRINT_NEWLINE       
             15 LOAD_CONST               0 (None)
             18 RETURN_VALUE 

>>> def compare(base, value):
...     return value > base
... 
>>> compare(10, 5)
False
>>> compare(10, 20)
True

>>> base = 1
>>> def get_compare(base):
...     def real_compare(value):
...         return value > base
...     return real_compare
... 
>>> compare_with_10 = get_compare(10)
>>> compare_with_10(5)
False
>>> compare_with_10(20)
True

# cat demo4.py 
def get_func():
    a = 1
    value = "inner"

    def inner_func():
        print(value)

    return inner_func

>>> source = open("demo4.py").read()
>>> co = compile(source, "demo4.py", "exec")
>>> co.co_consts
(, None)

>>> get_func_co = co.co_consts[0]
>>> get_func_co.co_name
‘get_func‘
>>> get_func_co.co_cellvars
(‘value‘,)

>>> get_func_co.co_consts
(None, 1, ‘inner‘, )
>>> inner_func_co = get_func_co.co_consts[3]
>>> inner_func_co.co_freevars
(‘value‘,)

ncells = PyTuple_GET_SIZE(code->co_cellvars);
nfrees = PyTuple_GET_SIZE(code->co_freevars);
extras = code->co_stacksize + code->co_nlocals + ncells + nfrees;

# cat demo5.py
def get_func():
    value = "inner"

    def inner_func():
        print(value)

    return inner_func


show_value = get_func()
show_value()

>>> source = open("demo5.py").read()
>>> co = compile(source, "demo5.py", "exec")
>>> import dis
>>> dis.dis(co)
  1           0 LOAD_CONST               0 ()
              3 MAKE_FUNCTION            0
              6 STORE_NAME               0 (get_func)

 10           9 LOAD_NAME                0 (get_func)
             12 CALL_FUNCTION            0
             15 STORE_NAME               1 (show_value)

 11          18 LOAD_NAME                1 (show_value)
             21 CALL_FUNCTION            0
             24 POP_TOP             
             25 LOAD_CONST               1 (None)
             28 RETURN_VALUE  

>>> co.co_consts
(, None)
>>> get_func_co = co.co_consts[0]
>>> get_func_co.co_flags
3
>>> dis.dis(get_func_co)
  2           0 LOAD_CONST               1 (‘inner‘)
              3 STORE_DEREF              0 (value)

  4           6 LOAD_CLOSURE             0 (value)
              9 BUILD_TUPLE              1
             12 LOAD_CONST               2 ()
             15 MAKE_CLOSURE             0
             18 STORE_FAST               0 (inner_func)

  7          21 LOAD_FAST                0 (inner_func)
             24 RETURN_VALUE 

>>> get_func_co.co_consts
(None, ‘inner‘, )
>>> inner_func_co = get_func_co.co_consts[2]
>>> inner_func_co.co_flags
19
>>> dis.dis(inner_func_co)
  5           0 LOAD_DEREF               0 (value)
              3 PRINT_ITEM          
              4 PRINT_NEWLINE       
              5 LOAD_CONST               0 (None)
              8 RETURN_VALUE  

PyObject *
PyEval_EvalCodeEx(PyCodeObject *co, PyObject *globals, PyObject *locals,
				  PyObject **args, int argcount, PyObject **kws, int kwcount,
				  PyObject **defs, int defcount, PyObject *closure)
{
	……
	if (PyTuple_GET_SIZE(co->co_cellvars))
	{
		int i, j, nargs, found;
		char *cellname, *argname;
		PyObject *c;

		nargs = co->co_argcount;
		if (co->co_flags & CO_VARARGS)
			nargs++;
		if (co->co_flags & CO_VARKEYWORDS)
			nargs++;

		for (i = 0; i co_cellvars); ++i)
		{
			//[1]：获得被嵌套函数共享的符号名
			cellname = PyString_AS_STRING(
				PyTuple_GET_ITEM(co->co_cellvars, i));
			found = 0;
			for (j = 0; j co_varnames, j));
				if (strcmp(cellname, argname) == 0)
				{
					c = PyCell_New(GETLOCAL(j));
					if (c == NULL)
						goto fail;
					GETLOCAL(co->co_nlocals + i) = c;
					found = 1;
					break;
				}
			}
			//处理被嵌套函数共享外层函数的默认参数
			if (found == 0)
			{
				c = PyCell_New(NULL);
				if (c == NULL)
					goto fail;
				SETLOCAL(co->co_nlocals + i, c);
			}
		}
	}
	……
}

typedef struct {
	PyObject_HEAD
	PyObject *ob_ref;	/* Content of the cell or NULL when empty */
} PyCellObject;

PyObject *
PyCell_New(PyObject *obj)
{
	PyCellObject *op;

	op = (PyCellObject *)PyObject_GC_New(PyCellObject, &PyCell_Type);
	if (op == NULL)
		return NULL;
	op->ob_ref = obj;
	Py_XINCREF(obj);

	_PyObject_GC_TRACK(op);
	return (PyObject *)op;
}

>>> dis.dis(get_func_co)
  2           0 LOAD_CONST               1 (‘inner‘)
              3 STORE_DEREF              0 (value)

  4           6 LOAD_CLOSURE             0 (value)
              9 BUILD_TUPLE              1
             12 LOAD_CONST               2 ()
             15 MAKE_CLOSURE             0
             18 STORE_FAST               0 (inner_func)

  7          21 LOAD_FAST                0 (inner_func)
             24 RETURN_VALUE 

PyObject * PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
{
	……
	freevars = f->f_localsplus + co->co_nlocals;
	……
}

case STORE_DEREF:
	w = POP();
	x = freevars[oparg];
	PyCell_Set(x, w);
	Py_DECREF(w);
	continue;

#define PyCell_SET(op, v) (((PyCellObject *)(op))->ob_ref = v)

int PyCell_Set(PyObject *op, PyObject *obj)
{
	if (!PyCell_Check(op)) {
		PyErr_BadInternalCall();
		return -1;
	}
	Py_XDECREF(((PyCellObject*)op)->ob_ref);
	Py_XINCREF(obj);
	PyCell_SET(op, obj);
	return 0;
}

case LOAD_CLOSURE:
	x = freevars[oparg];
	Py_INCREF(x);
	PUSH(x);
	if (x != NULL)
		continue;
	break;

case MAKE_CLOSURE:
	{
		v = POP(); //获得PyCodeObject对象
		x = PyFunction_New(v, f->f_globals);//绑定global名字空间
		Py_DECREF(v);
		if (x != NULL)
		{
			v = POP();//获得tupple，其中包含PyCellObject对象的集合
			err = PyFunction_SetClosure(x, v);//绑定约束集合
			Py_DECREF(v);
		}
		//处理拥有默认值的参数
		if (x != NULL && oparg > 0)
		{
			v = PyTuple_New(oparg);
			if (v == NULL)
			{
				Py_DECREF(x);
				x = NULL;
				break;
			}
			while (--oparg >= 0)
			{
				w = POP();
				PyTuple_SET_ITEM(v, oparg, w);
			}
			err = PyFunction_SetDefaults(x, v);
			Py_DECREF(v);
		}
		PUSH(x);
		break;
	}

>>> dis.dis(inner_func_co)
  5           0 LOAD_DEREF               0 (value)
              3 PRINT_ITEM          
              4 PRINT_NEWLINE       
              5 LOAD_CONST               0 (None)
              8 RETURN_VALUE 

PyObject *
PyEval_EvalCodeEx(PyCodeObject *co, PyObject *globals, PyObject *locals,
				  PyObject **args, int argcount, PyObject **kws, int kwcount,
				  PyObject **defs, int defcount, PyObject *closure)
{
	……
	if (PyTuple_GET_SIZE(co->co_freevars))
	{
		int i;
		for (i = 0; i co_freevars); ++i)
		{
			PyObject *o = PyTuple_GET_ITEM(closure, i);
			Py_INCREF(o);
			freevars[PyTuple_GET_SIZE(co->co_cellvars) + i] = o;
		}
	}
	……
}

//funcobject.c
#define PyFunction_GET_CLOSURE(func) 	(((PyFunctionObject *)func) -> func_closure)

	
//ceval.c
static PyObject *
fast_function(PyObject *func, PyObject ***pp_stack, int n, int na, int nk)
{
	……
	return PyEval_EvalCodeEx(co, globals,
							 (PyObject *)NULL, (*pp_stack) - n, na,
							 (*pp_stack) - 2 * nk, nk, d, nd,
							 PyFunction_GET_CLOSURE(func));
}

case LOAD_DEREF:
	x = freevars[oparg];//获得PyCellObject对象
	w = PyCell_Get(x);//获得PyCellObject.ob_obj指向的对象
	if (w != NULL)
	{
		PUSH(w);
		continue;
	}
	……

# cat demo6.py 
def should_say(fn):
    def say(*args):
        print("say something...")
        fn(*args)

    return say


@should_say
def func():
    print("in func")


func()
# python2.5 demo6.py 
say something...
in func

# cat demo7.py 
def should_say(fn):
    def say(*args):
        print("say something...")
        fn(*args)

    return say


def func():
    print("in func")


func = should_say(func)
func()
# python2.5 demo7.py 
say something...
in func

@should_say
def func():
    //字节码指令序列
	9 	LOAD_NAME                0 (should_say)
	12 	LOAD_CONST               1 ()
	15 	MAKE_FUNCTION            0
	18 	CALL_FUNCTION            1
	21 	STORE_NAME               1 (func)
    print("in func")

def func():
	//字节码指令序列
	9 	LOAD_CONST               1 ()
	12 	MAKE_FUNCTION            0
	15 	STORE_NAME               1 (func)
    print("in func")


func = should_say(func)
//字节码指令序列
18 	LOAD_NAME                0 (should_say)
21 	LOAD_NAME                1 (func)
24 	CALL_FUNCTION            1
27 	STORE_NAME               1 (func)