我正在尝试修改 Brandon Rhodes 代码 Routines that examine the internals of a CPython dictionary以便它适用于 CPython 3.3。
我相信我已经成功翻译了这个结构。
typedef PyDictKeyEntry *(*dict_lookup_func)
(PyDictObject *mp, PyObject *key, Py_hash_t hash, PyObject ***value_addr);
struct _dictkeysobject {
Py_ssize_t dk_refcnt;
Py_ssize_t dk_size;
dict_lookup_func dk_lookup;
Py_ssize_t dk_usable;
PyDictKeyEntry dk_entries[1];
};
我认为以下内容现在看起来不错:
from ctypes import Structure, c_ulong, POINTER, cast, py_object, CFUNCTYPE
LOOKUPFUNC = CFUNCTYPE(POINTER(PyDictKeyEntry), POINTER(PyDictObject),
py_object, c_ulong, POINTER(POINTER(py_object)))
class PyDictKeysObject(Structure):
"""A key object"""
_fields_ = [
('dk_refcnt', c_ssize_t),
('dk_size', c_ssize_t),
('dk_lookup', LOOKUPFUNC),
('dk_usable', c_ssize_t),
('dk_entries', PyDictKeyEntry * 1),
]
PyDictKeysObject._dk_entries = PyDictKeysObject.dk_entries
PyDictKeysObject.dk_entries = property(lambda s:
cast(s._dk_entries, POINTER(PyDictKeyEntry * s.dk_size))[0])
这行代码现在有效,其中 d == {0: 0, 1: 1, 2: 2, 3: 3}
:
obj = cast(id(d), POINTER(PyDictObject)).contents # works!!`
这是我对 C struct 的翻译PyDict对象:
class PyDictObject(Structure): # an incomplete type
"""A dictionary object."""
def __len__(self):
"""Return the number of dictionary entry slots."""
pass
def slot_of(self, key):
"""Find and return the slot at which `key` is stored."""
pass
def slot_map(self):
"""Return a mapping of keys to their integer slot numbers."""
pass
PyDictObject._fields_ = [
('ob_refcnt', c_ssize_t),
('ob_type', c_void_p),
('ma_used', c_ssize_t),
('ma_keys', POINTER(PyDictKeysObject)),
('ma_values', POINTER(py_object)), # points to array of ptrs
]
最佳答案
我的问题是访问在 Cpython 3.3 中实现的 python 字典下的 C 结构。我从 cpython/Objects/dictobject.c 和 Include/dictobject.h 中提供的 C 结构开始。定义字典时涉及三个 C 结构:PyDictObject、PyDictKeysObject 和 PyDictKeyEntry。每个 C 结构到 python 的正确翻译如下。评论指出了我需要修复的地方。感谢@eryksun 一路指导我!!
class PyDictKeyEntry(Structure):
"""An entry in a dictionary."""
_fields_ = [
('me_hash', c_ulong),
('me_key', py_object),
('me_value', py_object),
]
class PyDictObject(Structure):
"""A dictionary object."""
pass
LOOKUPFUNC = CFUNCTYPE(POINTER(PyDictKeyEntry), POINTER(PyDictObject), py_object, c_ulong, POINTER(POINTER(py_object)))
class PyDictKeysObject(Structure):
"""An object of key entries."""
_fields_ = [
('dk_refcnt', c_ssize_t),
('dk_size', c_ssize_t),
('dk_lookup', LOOKUPFUNC), # a function prototype per docs
('dk_usable', c_ssize_t),
('dk_entries', PyDictKeyEntry * 1), # an array of size 1; size grows as keys are inserted into dictionary; this variable-sized field was the trickiest part to translate into python
]
PyDictObject._fields_ = [
('ob_refcnt', c_ssize_t), # Py_ssize_t translates to c_ssize_t per ctypes docs
('ob_type', c_void_p), # could not find this in the docs
('ma_used', c_ssize_t),
('ma_keys', POINTER(PyDictKeysObject)),
('ma_values', POINTER(py_object)), # Py_Object* translates to py_object per ctypes docs
]
PyDictKeysObject._dk_entries = PyDictKeysObject.dk_entries
PyDictKeysObject.dk_entries = property(lambda s: cast(s._dk_entries, POINTER(PyDictKeyEntry * s.dk_size))[0]) # this line is called every time the attribute dk_entries is accessed by a PyDictKeyEntry instance; it returns an array of size dk_size starting at address _dk_entries. (POINTER creates a pointer to the entire array; the pointer is dereferenced (using [0]) to return the entire array); the code then accesses the ith element of the array)
以下函数提供对 python 字典底层的 PyDictObject 的访问:
def dictobject(d):
"""Return the PyDictObject lying behind the Python dict `d`."""
if not isinstance(d, dict):
raise TypeError('cannot create a dictobject from %r' % (d,))
return cast(id(d), POINTER(PyDictObject)).contents
如果 d 是具有键值对的 python 字典,则 obj 是包含键值对的 PyDictObject 实例:
obj = cast(id(d), POINTER(PyDictObject)).contents
PyDictKeysObject 的实例是:
key_obj = obj.ma_keys.contents
指向存储在字典槽 0 中的键的指针是:
key_obj.dk_entries[0].me_key
使用这些类的程序,连同探测插入字典的每个键的散列冲突的例程,位于here。 .我的代码是 Brandon Rhodes 为 python 2.x 编写的代码的修改。他的密码是here .
关于 python 3.3 字典 : how to convert struct PyDictKeysObject to python class?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/23328908/