概要
CPythonの基本となるPyObjectについて、簡潔に確認する。
内容
Python 3.x
PyObject
PyObject自体を使うことはないが、すべてのPython objectはPyObject*にcastできる。手作業での継承。
PyObject(cpython/Include/object.h)
typedef struct _object {
_PyObject_HEAD_EXTRA
Py_ssize_t ob_refcnt;
PyTypeObject *ob_type;
} PyObject;
-
_PyObject_HEAD_EXTRA: デバッグ版でなければ、空白に置き換えられる。 -
ob_refcnt: 参照カウント。 -
ob_type:PyTypeObjectへのポインタ。
PyTypeObject
PyTypeObject(cpython/Include/object.h)
typedef struct _typeobject PyTypeObject;
_typeobject(cpython/Include/cpython/object.h)
struct _typeobject {
PyObject_VAR_HEAD
const char *tp_name; /* For printing, in format "<module>.<name>" */
Py_ssize_t tp_basicsize, tp_itemsize; /* For allocation */
/* Methods to implement standard operations */
destructor tp_dealloc;
Py_ssize_t tp_vectorcall_offset;
getattrfunc tp_getattr;
setattrfunc tp_setattr;
PyAsyncMethods *tp_as_async; /* formerly known as tp_compare (Python 2)
or tp_reserved (Python 3) */
reprfunc tp_repr;
/* Method suites for standard classes */
PyNumberMethods *tp_as_number;
PySequenceMethods *tp_as_sequence;
PyMappingMethods *tp_as_mapping;
/* More standard operations (here for binary compatibility) */
hashfunc tp_hash;
ternaryfunc tp_call;
reprfunc tp_str;
getattrofunc tp_getattro;
setattrofunc tp_setattro;
/* Functions to access object as input/output buffer */
PyBufferProcs *tp_as_buffer;
/* Flags to define presence of optional/expanded features */
unsigned long tp_flags;
const char *tp_doc; /* Documentation string */
/* Assigned meaning in release 2.0 */
/* call function for all accessible objects */
traverseproc tp_traverse;
/* delete references to contained objects */
inquiry tp_clear;
/* Assigned meaning in release 2.1 */
/* rich comparisons */
richcmpfunc tp_richcompare;
/* weak reference enabler */
Py_ssize_t tp_weaklistoffset;
/* Iterators */
getiterfunc tp_iter;
iternextfunc tp_iternext;
/* Attribute descriptor and subclassing stuff */
struct PyMethodDef *tp_methods;
struct PyMemberDef *tp_members;
struct PyGetSetDef *tp_getset;
struct _typeobject *tp_base;
PyObject *tp_dict;
descrgetfunc tp_descr_get;
descrsetfunc tp_descr_set;
Py_ssize_t tp_dictoffset;
initproc tp_init;
allocfunc tp_alloc;
newfunc tp_new;
freefunc tp_free; /* Low-level free-memory routine */
inquiry tp_is_gc; /* For PyObject_IS_GC */
PyObject *tp_bases;
PyObject *tp_mro; /* method resolution order */
PyObject *tp_cache;
PyObject *tp_subclasses;
PyObject *tp_weaklist;
destructor tp_del;
/* Type attribute cache version tag. Added in version 2.6 */
unsigned int tp_version_tag;
destructor tp_finalize;
vectorcallfunc tp_vectorcall;
};
ここに様々な振る舞いが描かれている。
PyObject_VAR_HEAD
PyObject_VAR_HEAD(cpython/Include/object.h)
#define PyObject_VAR_HEAD PyVarObject ob_base;
...
typedef struct {
PyObject ob_base;
Py_ssize_t ob_size; /* Number of items in variable part */
} PyVarObject;
使用例(PyDictObject)
PyDictObject(cpython/Include/cpython/dictobject.h)
typedef struct {
PyObject_HEAD
/* Number of items in the dictionary */
Py_ssize_t ma_used;
/* Dictionary version: globally unique, value change each time
the dictionary is modified */
uint64_t ma_version_tag;
PyDictKeysObject *ma_keys;
/* If ma_values is NULL, the table is "combined": keys and values
are stored in ma_keys.
If ma_values is not NULL, the table is splitted:
keys are stored in ma_keys and values are stored in ma_values */
PyObject **ma_values;
} PyDictObject;
PyObject_HEADは下記の通りであり、実際に継承している。
#define PyObject_HEAD PyObject ob_base;
PyDict_Type(cpython/Objects/dictobject.h)
PyTypeObject PyDict_Type = {
PyVarObject_HEAD_INIT(&PyType_Type, 0)
"dict",
sizeof(PyDictObject),
0,
(destructor)dict_dealloc, /* tp_dealloc */
0, /* tp_vectorcall_offset */
0, /* tp_getattr */
0, /* tp_setattr */
0, /* tp_as_async */
(reprfunc)dict_repr, /* tp_repr */
&dict_as_number, /* tp_as_number */
&dict_as_sequence, /* tp_as_sequence */
&dict_as_mapping, /* tp_as_mapping */
PyObject_HashNotImplemented, /* tp_hash */
0, /* tp_call */
0, /* tp_str */
PyObject_GenericGetAttr, /* tp_getattro */
0, /* tp_setattro */
0, /* tp_as_buffer */
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
Py_TPFLAGS_BASETYPE | Py_TPFLAGS_DICT_SUBCLASS, /* tp_flags */
dictionary_doc, /* tp_doc */
dict_traverse, /* tp_traverse */
dict_tp_clear, /* tp_clear */
dict_richcompare, /* tp_richcompare */
0, /* tp_weaklistoffset */
(getiterfunc)dict_iter, /* tp_iter */
0, /* tp_iternext */
mapp_methods, /* tp_methods */
0, /* tp_members */
0, /* tp_getset */
0, /* tp_base */
0, /* tp_dict */
0, /* tp_descr_get */
0, /* tp_descr_set */
0, /* tp_dictoffset */
dict_init, /* tp_init */
PyType_GenericAlloc, /* tp_alloc */
dict_new, /* tp_new */
PyObject_GC_Del, /* tp_free */
.tp_vectorcall = dict_vectorcall,
};
辞書生成は、下記の通り。
(cpython/Objects/dictobject.c)
/* Consumes a reference to the keys object */
static PyObject *
new_dict(PyDictKeysObject *keys, PyObject **values)
{
PyDictObject *mp;
assert(keys != NULL);
struct _Py_dict_state *state = get_dict_state();
...
if (state->numfree) {
mp = state->free_list[--state->numfree];
assert (mp != NULL);
assert (Py_IS_TYPE(mp, &PyDict_Type));
_Py_NewReference((PyObject *)mp);
}
else {
mp = PyObject_GC_New(PyDictObject, &PyDict_Type);
if (mp == NULL) {
dictkeys_decref(keys);
if (values != empty_values) {
free_values(values);
}
return NULL;
}
}
mp->ma_keys = keys;
mp->ma_values = values;
mp->ma_used = 0;
mp->ma_version_tag = DICT_NEXT_VERSION();
ASSERT_CONSISTENT(mp);
return (PyObject *)mp;
}
蛇足
(cpython/Include/object.h)
#define _PyObject_CAST_CONST(op) ((const PyObject*)(op))
...
static inline Py_ssize_t _Py_REFCNT(const PyObject *ob) {
return ob->ob_refcnt;
}
#define Py_REFCNT(ob) _Py_REFCNT(_PyObject_CAST_CONST(ob))
static inline Py_ssize_t _Py_SIZE(const PyVarObject *ob) {
return ob->ob_size;
}
#define Py_SIZE(ob) _Py_SIZE(_PyVarObject_CAST_CONST(ob))
static inline PyTypeObject* _Py_TYPE(const PyObject *ob) {
return ob->ob_type;
}
#define Py_TYPE(ob) _Py_TYPE(_PyObject_CAST_CONST(ob))
-
Py_REFCNT(ob):ob_refcntを得るマクロ。 -
Py_SIZE(ob):ob_sizeを得るマクロ。 -
Py_TYPE(ob):ob_typeを得るマクロ。
(const PyObject*)にキャストした後に得ている。
参考にさせて頂いた本・ページ
感想
落ち着いてまとめられたことがなかったので、よかった。