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通用对象结构

通用对象结构 ¶

Python 对象类型定义使用了大量 Structure。此节描述这些 Structure 及如何使用它们。

基对象类型和宏 ¶

All Python objects ultimately share a small number of fields at the beginning of the object’s representation in memory. These are represented by the PyObject and PyVarObject types, which are defined, in turn, by the expansions of some macros also used, whether directly or indirectly, in the definition of all other Python objects. Additional macros can be found under reference counting .

type PyObject ¶: 属于 Limited API . (Only some members are part of the stable ABI.)
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 .

type PyVarObject ¶: 属于 Limited API . (Only some members are part of the stable ABI.)
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 ，和 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:

PyObject ob_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:

PyVarObject ob_base;

See documentation of PyVarObject above.

int Py_Is ( PyObject * x , PyObject * y ) ¶

属于稳定 ABI (应用程序二进制接口) since version 3.10.

Test if the x 对象是 y object, the same as x is y in Python.

Added in version 3.10.

int Py_IsNone ( PyObject * x ) ¶

属于稳定 ABI (应用程序二进制接口) since version 3.10.

Test if an object is the None singleton, the same as x is None in Python.

Added in version 3.10.

int Py_IsTrue ( PyObject * x ) ¶

属于稳定 ABI (应用程序二进制接口) since version 3.10.

Test if an object is the True singleton, the same as x is True in Python.

Added in version 3.10.

int Py_IsFalse ( PyObject * x ) ¶

属于稳定 ABI (应用程序二进制接口) since version 3.10.

Test if an object is the False singleton, the same as x is False in Python.

Added in version 3.10.

PyTypeObject * Py_TYPE ( PyObject * o ) ¶

Get the type of the Python object o .

返回借位引用 .

使用 Py_SET_TYPE() function to set an object type.

3.11 版改变： Py_TYPE() is changed to an inline static function. The parameter type is no longer const PyObject * .

int Py_IS_TYPE ( PyObject * o , PyTypeObject * type ) ¶

Return non-zero if the object o 类型为 type . Return zero otherwise. Equivalent to: Py_TYPE(o) == type .

Added in version 3.9.

void Py_SET_TYPE ( PyObject * o , PyTypeObject * type ) ¶

设置对象 o 类型到 type .

Added in version 3.9.

Py_ssize_t Py_SIZE ( PyVarObject * o ) ¶

Get the size of the Python object o .

使用 Py_SET_SIZE() function to set an object size.

3.11 版改变： Py_SIZE() is changed to an inline static function. The parameter type is no longer const PyVarObject * .

void Py_SET_SIZE ( PyVarObject * o , Py_ssize_t size ) ¶

设置对象 o size to size .

Added in version 3.9.

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,

实现函数和方法 ¶

type PyCFunction ¶

属于稳定 ABI (应用程序二进制接口) .

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.

The function signature is:

PyObject *PyCFunction(PyObject *self,
                      PyObject *args);

type PyCFunctionWithKeywords ¶

属于稳定 ABI (应用程序二进制接口) .

Type of the functions used to implement Python callables in C with signature METH_VARARGS | METH_KEYWORDS . The function signature is:

PyObject *PyCFunctionWithKeywords(PyObject *self,
                                  PyObject *args,
                                  PyObject *kwargs);

type _PyCFunctionFast ¶

Type of the functions used to implement Python callables in C with signature METH_FASTCALL . The function signature is:

PyObject *_PyCFunctionFast(PyObject *self,
                           PyObject *const *args,
                           Py_ssize_t nargs);

type _PyCFunctionFastWithKeywords ¶

Type of the functions used to implement Python callables in C with signature METH_FASTCALL | METH_KEYWORDS . The function signature is:

PyObject *_PyCFunctionFastWithKeywords(PyObject *self,
                                       PyObject *const *args,
                                       Py_ssize_t nargs,
                                       PyObject *kwnames);

type PyCMethod ¶

Type of the functions used to implement Python callables in C with signature METH_METHOD | METH_FASTCALL | METH_KEYWORDS . The function signature is:

PyObject *PyCMethod(PyObject *self,
                    PyTypeObject *defining_class,
                    PyObject *const *args,
                    Py_ssize_t nargs,
                    PyObject *kwnames)

Added in version 3.9.

type PyMethodDef ¶

属于稳定 ABI (应用程序二进制接口) (including all members).

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

const char * ml_name ¶: Name of the method.

PyCFunction ml_meth ¶: Pointer to the C implementation.

int ml_flags ¶: Flags bits indicating how the call should be constructed.

const char * ml_doc ¶: 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 对象。

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 these 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_KEYWORDS ¶: Can only be used in certain combinations with other flags: METH_VARARGS | METH_KEYWORDS , METH_FASTCALL | METH_KEYWORDS and METH_METHOD | METH_FASTCALL | METH_KEYWORDS .

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).

Added in version 3.7.

3.10 版改变： METH_FASTCALL is now part of the stable ABI .

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 (which are guaranteed to be strings) or possibly NULL if there are no keywords. The values of the keyword arguments are stored in the args array, after the positional arguments.

Added in version 3.7.

METH_METHOD ¶: Can only be used in the combination with other flags: METH_METHOD | METH_FASTCALL | METH_KEYWORDS .

METH_METHOD | METH_FASTCALL | METH_KEYWORDS

Extension of METH_FASTCALL | METH_KEYWORDS supporting the defining class , that is, the class that contains the method in question. The defining class might be a superclass of Py_TYPE(self) .

The method needs to be of type PyCMethod , the same as for METH_FASTCALL | METH_KEYWORDS with defining_class argument added after self .

Added in version 3.9.

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 .

The function must have 2 parameters. Since the second parameter is unused, Py_UNUSED can be used to prevent a compiler warning.

METH_O ¶: Methods with a single object argument can be listed with the METH_O flag, instead of invoking PyArg_ParseTuple() 采用 "O" argument. They have the type PyCFunction ，采用 self 参数，和 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() 内置函数。

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() 内置函数。

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.

PyObject * PyCMethod_New ( PyMethodDef * ml , PyObject * self , PyObject * 模块 , PyTypeObject * cls ) ¶

返回值：新引用。 属于稳定 ABI (应用程序二进制接口) since version 3.9.

Turn ml into a Python callable object. The caller must ensure that ml outlives the callable . Typically, ml is defined as a static variable.

The self parameter will be passed as the self argument to the C function in ml->ml_meth when invoked. self 可以是 NULL .

The callable 对象的 __module__ attribute can be set from the given 模块自变量。模块 should be a Python string, which will be used as name of the module the function is defined in. If unavailable, it can be set to None or NULL .

另请参阅

function.__module__

The cls parameter will be passed as the defining_class argument to the C function. Must be set if METH_METHOD is set on ml->ml_flags .

Added in version 3.9.

PyObject * PyCFunction_NewEx ( PyMethodDef * ml , PyObject * self , PyObject * 模块 ) ¶: 返回值：新引用。 属于稳定 ABI (应用程序二进制接口) .
相当于 PyCMethod_New(ml, self, module, NULL) .

PyObject * PyCFunction_New ( PyMethodDef * ml , PyObject * self ) ¶: 返回值：新引用。 属于稳定 ABI (应用程序二进制接口) since version 3.4.
相当于 PyCMethod_New(ml, self, NULL, NULL) .

访问扩展类型的属性 ¶

type PyMemberDef ¶

属于稳定 ABI (应用程序二进制接口) (including all members).

Structure which describes an attribute of a type which corresponds to a C struct member. When defining a class, put a NULL-terminated array of these structures in the tp_members 槽。

Its fields are, in order:

const char * name ¶

Name of the member. A NULL value marks the end of a PyMemberDef[] array.

The string should be static, no copy is made of it.

int type ¶: The type of the member in the C struct. See Member types for the possible values.

Py_ssize_t offset ¶: The offset in bytes that the member is located on the type’s object struct.

int flags ¶: Zero or more of the Member flags , combined using bitwise OR.

const char * doc ¶: The docstring, or NULL. The string should be static, no copy is made of it. Typically, it is defined using PyDoc_STR .

By default (when flags is 0 ), members allow both read and write access. Use the Py_READONLY flag for read-only access. Certain types, like Py_T_STRING , imply Py_READONLY . Only Py_T_OBJECT_EX (and legacy T_OBJECT ) members can be deleted.

For heap-allocated types (created using PyType_FromSpec() or similar), PyMemberDef may contain a definition for the special member "__vectorcalloffset__" , corresponding to tp_vectorcall_offset in type objects. These must be defined with Py_T_PYSSIZET and Py_READONLY ，例如：

static PyMemberDef spam_type_members[] = {
    {"__vectorcalloffset__", Py_T_PYSSIZET,
     offsetof(Spam_object, vectorcall), Py_READONLY},
    {NULL}  /* Sentinel */
};

(You may need to #include <stddef.h> for offsetof() )。

The legacy offsets tp_dictoffset and tp_weaklistoffset can be defined similarly using "__dictoffset__" and "__weaklistoffset__" members, but extensions are strongly encouraged to use Py_TPFLAGS_MANAGED_DICT and Py_TPFLAGS_MANAGED_WEAKREF 代替。

Changed in version 3.12: PyMemberDef is always available. Previously, it required including "structmember.h" .

PyObject * PyMember_GetOne ( const char * obj_addr , struct PyMemberDef * m ) ¶

属于稳定 ABI (应用程序二进制接口) .

Get an attribute belonging to the object at address obj_addr . The attribute is described by PyMemberDef m 。返回 NULL 当出错时。

Changed in version 3.12: PyMember_GetOne is always available. Previously, it required including "structmember.h" .

int PyMember_SetOne ( char * obj_addr , struct PyMemberDef * m , PyObject * o ) ¶

属于稳定 ABI (应用程序二进制接口) .

Set an attribute belonging to the object at address obj_addr to object o . The attribute to set is described by PyMemberDef m 。返回 0 if successful and a negative value on failure.

Changed in version 3.12: PyMember_SetOne is always available. Previously, it required including "structmember.h" .

Member flags ¶

The following flags can be used with PyMemberDef.flags :

Py_READONLY ¶: Not writable.

Py_AUDIT_READ ¶: Emit an object.__getattr__ audit event before reading.

Py_RELATIVE_OFFSET ¶

Indicates that the offset of this PyMemberDef entry indicates an offset from the subclass-specific data, rather than from PyObject .

Can only be used as part of Py_tp_members slot when creating a class using negative basicsize . It is mandatory in that case.

This flag is only used in PyType_Slot . When setting tp_members during class creation, Python clears it and sets PyMemberDef.offset to the offset from the PyObject struct.

3.10 版改变： The RESTRICTED , READ_RESTRICTED and WRITE_RESTRICTED macros available with #include "structmember.h" 被弃用。 READ_RESTRICTED and RESTRICTED are equivalent to Py_AUDIT_READ ; WRITE_RESTRICTED 什么都不做。

Changed in version 3.12: The READONLY macro was renamed to Py_READONLY 。 PY_AUDIT_READ macro was renamed with the Py_ prefix. The new names are now always available. Previously, these required #include "structmember.h" . The header is still available and it provides the old names.

Member types ¶

PyMemberDef.type can be one of the following macros corresponding to various C types. When the member is accessed in Python, it will be converted to the equivalent Python type. When it is set from Python, it will be converted back to the C type. If that is not possible, an exception such as TypeError or ValueError 被引发。

Unless marked (D), attributes defined this way cannot be deleted using e.g. del or delattr() .

Macro name	C 类型	Python 类型
Py_T_BYTE ¶	char	`int`
Py_T_SHORT ¶	short	`int`
Py_T_INT ¶	int	`int`
Py_T_LONG ¶	long	`int`
Py_T_LONGLONG ¶	long long	`int`
Py_T_UBYTE ¶	unsigned char	`int`
Py_T_UINT ¶	unsigned int	`int`
Py_T_USHORT ¶	unsigned short	`int`
Py_T_ULONG ¶	unsigned long	`int`
Py_T_ULONGLONG ¶	unsigned long long	`int`
Py_T_PYSSIZET ¶	Py_ssize_t	`int`
Py_T_FLOAT ¶	float	`float`
Py_T_DOUBLE ¶	double	`float`
Py_T_BOOL ¶	char (written as 0 or 1)	`bool`
Py_T_STRING ¶	const char * (*)	`str` (RO)
Py_T_STRING_INPLACE ¶	const char [ ] (*)	`str` (RO)
Py_T_CHAR ¶	char (0-127)	`str` (**)
Py_T_OBJECT_EX ¶	PyObject *	`object` (D)

(*): Zero-terminated, UTF8-encoded C string. With Py_T_STRING the C representation is a pointer; with Py_T_STRING_INPLACE the string is stored directly in the structure.

(**): String of length 1. Only ASCII is accepted.

(RO): Implies Py_READONLY .

(D): Can be deleted, in which case the pointer is set to NULL . Reading a NULL pointer raises AttributeError .

Added in version 3.12: In previous versions, the macros were only available with #include "structmember.h" and were named without the Py_ prefix (e.g. as T_INT ). The header is still available and contains the old names, along with the following deprecated types:

T_OBJECT ¶: 像 Py_T_OBJECT_EX ，但 NULL 被转换成 None . This results in surprising behavior in Python: deleting the attribute effectively sets it to None .

T_NONE ¶: Always None . Must be used with Py_READONLY .

Defining Getters and Setters ¶

type PyGetSetDef ¶

属于稳定 ABI (应用程序二进制接口) (including all members).

Structure to define property-like access for a type. See also description of the PyTypeObject.tp_getset 槽。

const char * name ¶: attribute name

getter get ¶: C function to get the attribute.

setter set ¶: Optional C function to set or delete the attribute. If NULL , the attribute is read-only.

const char * doc ¶: optional docstring

void * closure ¶: Optional user data pointer, providing additional data for getter and setter.

typedef PyObject * ( * getter ) ( PyObject * , void * ) ¶

属于稳定 ABI (应用程序二进制接口) .

The get function takes one PyObject * parameter (the instance) and a user data pointer (the associated closure ):

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

typedef int ( * setter ) ( PyObject * , PyObject * , void * ) ¶

属于稳定 ABI (应用程序二进制接口) .

set functions take two PyObject * parameters (the instance and the value to be set) and a user data pointer (the associated closure ):

In case the attribute should be deleted the second parameter is NULL . Should return 0 当成功时或 -1 with a set exception on failure.