Python整数对象实现原理详解

typedef struct {
PyObject_HEAD
long ob_ival;
} PyIntObject;

int ob_refcnt; 
struct _typeobject *ob_type;

#define NSMALLPOSINTS 257
#define NSMALLNEGINTS 5
static PyIntObject *small_ints[NSMALLNEGINTS + NSMALLPOSINTS];

>>> a = 10000
>>> b = 10000
>>> print a is b
False
>>> a = 1
>>> b = 1
>>> print a is b
True

struct _intblock {
struct _intblock *next;
PyIntObject objects[N_INTOBJECTS];
};
typedef struct _intblock PyIntBlock;
static PyIntBlock *block_list = NULL;
static PyIntObject *free_list = NULL;

[intobject.c]
PyObject* PyInt_FromLong(long ival)
{
register PyIntObject *v; 
#if NSMALLNEGINTS + NSMALLPOSINTS > 0
//[1] ：尝试使用小整数对象池
if (-NSMALLNEGINTS <= ival && ival < NSMALLPOSINTS) {
v = small_ints[ival + NSMALLNEGINTS];
Py_INCREF(v);
return (PyObject *) v;
}
#endif
//[2] ：为通用整数对象池申请新的内存空间
if (free_list == NULL) {
if ((free_list = fill_free_list()) == NULL)
return NULL;
}
//[3] : (inline)内联PyObject_New的行为
v = free_list;
free_list = (PyIntObject *)v->ob_type;
PyObject_INIT(v, &PyInt_Type);
v->ob_ival = ival;
return (PyObject *) v;
}

[intobject.c]
static PyIntObject* fill_free_list(void)
{
PyIntObject *p, *q;
// 申请大小为sizeof(PyIntBlock)的内存空间
// block list始终指向最新创建的PyIntBlock
p = (PyIntObject *) PyMem_MALLOC(sizeof(PyIntBlock));
((PyIntBlock *)p)->next = block_list;
block_list = (PyIntBlock *)p;
//：将PyIntBlock中的PyIntObject数组(objects)转变成单向链表
p = &((PyIntBlock *)p)->objects[0];
q = p + N_INTOBJECTS;
while (--q > p)
// ob_type指向下一个未被使用的PyIntObject。
q->ob_type = (struct _typeobject *)(q-1);
q->ob_type = NULL;
return p + N_INTOBJECTS - 1;
}

[intobject.c]
static void int_dealloc(PyIntObject *v)
{
if (PyInt_CheckExact(v)) {
v->ob_type = (struct _typeobject *)free_list;
free_list = v;
}
else
v->ob_type->tp_free((PyObject *)v);
}