Python公用对象的结构

• Z时代
• 2024-01-10
• 分类：综合

大量的结构体被用于定义Python的对象类型。这一节描述了这些的结构体和它们的使用方法。

所有的 Python 对象都在对象的内存表示的开始部分共享少量的字段。 这些字段用 PyObject 或 PyVarObject 类型来表示，这些类型又由一些宏定义，这些宏也直接或间接地用于所有其他 Python 对象的定义。

PyObject¶

All object types are extensions of this type. This is a type which

contains the information Python needs to treat a pointer to an object as an

object. In a normal "release" build, it contains only the object's

reference count and a pointer to the corresponding type object.

Nothing is actually declared to be a PyObject, but every pointer

to a Python object can be cast to a PyObject*. Access to the

members must be done by using the macros Py_REFCNT and

Py_TYPE.

PyVarObject¶

This is an extension of PyObject that adds the ob_size

field. This is only used for objects that have some notion of length.

This type does not often appear in the Python/C API.

Access to the members must be done by using the macros

Py_REFCNT, Py_TYPE, and Py_SIZE.

PyObject_HEAD¶

This is a macro used when declaring new types which represent objects

without a varying length. The PyObject_HEAD macro expands to:

PyObjectob_base;

See documentation of PyObject above.

PyObject_VAR_HEAD¶

This is a macro used when declaring new types which represent objects

with a length that varies from instance to instance.

The PyObject_VAR_HEAD macro expands to:

PyVarObjectob_base;

See documentation of PyVarObject above.

Py_TYPE(o)¶

This macro is used to access the ob_type member of a Python object.

It expands to:

(((PyObject*)(o))->ob_type)

Py_REFCNT(o)¶

This macro is used to access the ob_refcnt member of a Python

object.

It expands to:

(((PyObject*)(o))->ob_refcnt)

Py_SIZE(o)¶

This macro is used to access the ob_size member of a Python object.

It expands to:

(((PyVarObject*)(o))->ob_size)

PyObject_HEAD_INIT(type)¶

This is a macro which expands to initialization values for a new

PyObject type. This macro expands to:

_PyObject_EXTRA_INIT
1,type,

PyVarObject_HEAD_INIT(type, size)¶

This is a macro which expands to initialization values for a new

PyVarObject type, including the ob_size field.

This macro expands to:

_PyObject_EXTRA_INIT
1,type,size,

PyCFunction¶

Type of the functions used to implement most Python callables in C.

Functions of this type take two PyObject* parameters and return

one such value. If the return value is NULL, an exception shall have

been set. If not NULL, the return value is interpreted as the return

value of the function as exposed in Python. The function must return a new

reference.

PyCFunctionWithKeywords¶

Type of the functions used to implement Python callables in C

with signature METH_VARARGS|METH_KEYWORDS.

_PyCFunctionFast¶

Type of the functions used to implement Python callables in C

with signature METH_FASTCALL.

_PyCFunctionFastWithKeywords¶

Type of the functions used to implement Python callables in C

with signature METH_FASTCALL|METH_KEYWORDS.

PyMethodDef¶

Structure used to describe a method of an extension type. This structure has

four fields:

域	C 类型	含义
ml_name	const char *	name of the method
ml_meth	PyCFunction	pointer to the C implementation
ml_flags	整型	flag bits indicating how the call should be constructed
ml_doc	const char *	points to the contents of the docstring

The ml_meth is a C function pointer. The functions may be of different

types, but they always return PyObject*. If the function is not of

the PyCFunction, the compiler will require a cast in the method table.

Even though PyCFunction defines the first parameter as

PyObject*, it is common that the method implementation uses the

specific C type of the self object.

The ml_flags field is a bitfield which can include the following flags.

The individual flags indicate either a calling convention or a binding

convention.

There are four basic calling conventions for positional arguments

and two of them can be combined with METH_KEYWORDS to support

also keyword arguments. So there are a total of 6 calling conventions:

METH_VARARGS¶

This is the typical calling convention, where the methods have the type

PyCFunction. The function expects two PyObject* values.

The first one is the self object for methods; for module functions, it is

the module object. The second parameter (often called args) is a tuple

object representing all arguments. This parameter is typically processed

using PyArg_ParseTuple() or PyArg_UnpackTuple().

METH_VARARGS | METH_KEYWORDS

Methods with these flags must be of type PyCFunctionWithKeywords.

The function expects three parameters: self, args, kwargs where

kwargs is a dictionary of all the keyword arguments or possibly NULL

if there are no keyword arguments. The parameters are typically processed

using PyArg_ParseTupleAndKeywords().

METH_FASTCALL¶

Fast calling convention supporting only positional arguments.

The methods have the type _PyCFunctionFast.

The first parameter is self, the second parameter is a C array

of PyObject* values indicating the arguments and the third

parameter is the number of arguments (the length of the array).

This is not part of the limited API.

3.7 新版功能.

METH_FASTCALL | METH_KEYWORDS

Extension of METH_FASTCALL supporting also keyword arguments,

with methods of type _PyCFunctionFastWithKeywords.

Keyword arguments are passed the same way as in the vectorcall protocol:

there is an additional fourth PyObject* parameter

which is a tuple representing the names of the keyword arguments

or possibly NULL if there are no keywords. The values of the keyword

arguments are stored in the args array, after the positional arguments.

This is not part of the limited API.

3.7 新版功能.

METH_NOARGS¶

Methods without parameters don't need to check whether arguments are given if

they are listed with the METH_NOARGS flag. They need to be of type

PyCFunction. The first parameter is typically named self and will

hold a reference to the module or object instance. In all cases the second

parameter will be NULL.

METH_O¶

Methods with a single object argument can be listed with the METH_O

flag, instead of invoking PyArg_ParseTuple() with a "O" argument.

They have the type PyCFunction, with the self parameter, and a

PyObject* parameter representing the single argument.

These two constants are not used to indicate the calling convention but the

binding when use with methods of classes. These may not be used for functions

defined for modules. At most one of these flags may be set for any given

method.

METH_CLASS¶

The method will be passed the type object as the first parameter rather

than an instance of the type. This is used to create class methods,

similar to what is created when using the classmethod() built-in

function.

METH_STATIC¶

The method will be passed NULL as the first parameter rather than an

instance of the type. This is used to create static methods, similar to

what is created when using the staticmethod() built-in function.

One other constant controls whether a method is loaded in place of another

definition with the same method name.

METH_COEXIST¶

The method will be loaded in place of existing definitions. Without

METH_COEXIST, the default is to skip repeated definitions. Since slot

wrappers are loaded before the method table, the existence of a

sq_contains slot, for example, would generate a wrapped method named

__contains__() and preclude the loading of a corresponding

PyCFunction with the same name. With the flag defined, the PyCFunction

will be loaded in place of the wrapper object and will co-exist with the

slot. This is helpful because calls to PyCFunctions are optimized more

than wrapper object calls.

PyMemberDef¶

Structure which describes an attribute of a type which corresponds to a C

struct member. Its fields are:

域	C 类型	含义
name	const char *	name of the member
type	整型	the type of the member in the C struct
offset	Py_ssize_t	the offset in bytes that the member is located on the type's object struct
flags	整型	flag bits indicating if the field should be read-only or writable
doc	const char *	points to the contents of the docstring

type can be one of many T_ macros corresponding to various C

types. When the member is accessed in Python, it will be converted to the

equivalent Python type.

Macro name	C 类型
T_SHORT	short
T_INT	整型
T_LONG	长整型
T_FLOAT	浮点数
T_DOUBLE	double
T_STRING	const char *
T_OBJECT	PyObject *
T_OBJECT_EX	PyObject *
T_CHAR	字符
T_BYTE	字符
T_UBYTE	unsigned char
T_UINT	无符号整型
T_USHORT	unsigned short
T_ULONG	无符号长整型
T_BOOL	字符
T_LONGLONG	long long
T_ULONGLONG	无符号 long long
T_PYSSIZET	Py_ssize_t

T_OBJECT and T_OBJECT_EX differ in that

T_OBJECT returns None if the member is NULL and

T_OBJECT_EX raises an AttributeError. Try to use

T_OBJECT_EX over T_OBJECT because T_OBJECT_EX

handles use of the del statement on that attribute more correctly

than T_OBJECT.

flags can be 0 for write and read access or READONLY for

read-only access. Using T_STRING for type implies

READONLY. T_STRING data is interpreted as UTF-8.

Only T_OBJECT and T_OBJECT_EX

members can be deleted. (They are set to NULL).

PyGetSetDef¶

Structure to define property-like access for a type. See also description of

the PyTypeObject.tp_getset slot.

域	C 类型	含义
名称	const char *	attribute name
get	getter	C Function to get the attribute
set	setter	optional C function to set or delete the attribute, if omitted the attribute is readonly
doc	const char *	optional docstring
closure	void *	optional function pointer, providing additional data for getter and setter

The get function takes one PyObject* parameter (the

instance) and a function pointer (the associated closure):

typedefPyObject*(*getter)(PyObject*,void*);

It should return a new reference on success or NULL with a set exception

on failure.

set functions take two PyObject* parameters (the instance and

the value to be set) and a function pointer (the associated closure):

typedefint(*setter)(PyObject*,PyObject*,void*);

In case the attribute should be deleted the second parameter is NULL.

Should return 0 on success or -1 with a set exception on failure.