# Estructuras de objetos comunes

Hay un gran número de estructuras que se utilizan en la definición de los tipos de objetos de Python. Esta sección describe estas estructuras y la forma en que se utilizan.

## Tipos objeto base y macros

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
  Part of the 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
  Part of the 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`, and `Py_SIZE`.

PyObject_HEAD

  Esta es una macro utilizado cuando se declara nuevos tipos que representan objetos sin una longitud variable. La macro PyObject_HEAD se expande a:

      PyObject ob_base;

  Consulte la documentación de `PyObject` en secciones anteriores.

PyObject_VAR_HEAD

  Esta es una macro utilizado cuando se declara nuevos tipos que representan objetos con una longitud que varía de una instancia a otra instancia. La macro PyObject_VAR_HEAD se expande a:

      PyVarObject ob_base;

  Consulte la documentación de `PyVarObject` anteriormente.

int Py_Is(PyObject *x, PyObject *y)
  Part of the Stable ABI since version 3.10.

  Prueba si el objeto x es el objeto y, lo mismo que `x is y` en Python.

  Added in version 3.10.

int Py_IsNone(PyObject *x)
  Part of the Stable ABI since version 3.10.

  Prueba si un objeto es la instancia única `None`, lo mismo que `x is None` en Python.

  Added in version 3.10.

int Py_IsTrue(PyObject *x)
  Part of the Stable ABI since version 3.10.

  Prueba si un objeto es la instancia única `True`, lo mismo que `x is True` en Python.

  Added in version 3.10.

int Py_IsFalse(PyObject *x)
  Part of the Stable ABI since version 3.10.

  Prueba si un objeto es la instancia única `False`, lo mismo que `x is False` en Python.

  Added in version 3.10.

PyTypeObject *Py_TYPE(PyObject *o)

  Obtiene el tipo de objeto Python o.

  Retorna una referencia prestada (borrowed reference).

  Use the `Py_SET_TYPE()` function to set an object type.

  Distinto en la versión 3.11: `Py_TYPE()` se cambia a una función estática inline. El tipo de parámetro ya no es const PyObject*.

int Py_IS_TYPE(PyObject *o, PyTypeObject *type)

  Retorna un valor distinto de cero si el objeto o tipo es type. Retorna cero en caso contrario. Equivalente a: `Py_TYPE(o) == type`.

  Added in version 3.9.

void Py_SET_TYPE(PyObject *o, PyTypeObject *type)

  Establece el tipo del objeto o a type.

  Added in version 3.9.

Py_ssize_t Py_SIZE(PyVarObject *o)

  Obtiene el tamaño del objeto Python o.

  Use the `Py_SET_SIZE()` function to set an object size.

  Distinto en la versión 3.11: `Py_SIZE()` se cambia a una función estática inline. El tipo de parámetro ya no es const PyVarObject*.

void Py_SET_SIZE(PyVarObject *o, Py_ssize_t size)

  Establece el tamaño del objeto o a size.

  Added in version 3.9.

PyObject_HEAD_INIT(type)

  Esta es una macro que se expande para valores de inicialización para un nuevo tipo `PyObject`. Esta macro expande:

      _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,

## Implementando funciones y métodos

type PyCFunction
  Part of the Stable ABI.

  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.

  La firma de la función es:

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

type PyCFunctionWithKeywords
  Part of the Stable ABI.

  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
  Part of the Stable ABI (including all members).

  Estructura utiliza para describir un método de un tipo de extensión. Esta estructura tiene cuatro campos:

  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 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.

Existen estas convenciones de llamada:

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

  Los métodos con estas flags deben ser del tipo `PyCFunctionWithKeywords`. La función espera tres parámetros: self, args, kwargs donde kwargs es un diccionario de todos los argumentos de palabras clave o, posiblemente, `NULL` si no hay argumentos de palabra clave. Los parámetros se procesan típicamente usando `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.

  Distinto en la versión 3.10: `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)`.

  El método debe ser de tipo `PyCMethod`, lo mismo que para `METH_FASTCALL | METH_KEYWORDS` con el argumento `defining_clase` añadido después de `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`.

  La función debe tener 2 parámetros. Dado que el segundo parámetro no se usa, `Py_UNUSED` se puede usar para evitar una advertencia del compilador.

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.

Estas dos constantes no se utilizan para indicar la convención de llamada si no la vinculación cuando su usan con métodos de las clases. Estos no se pueden usar para funciones definidas para módulos. A lo sumo uno de estos flags puede establecerse en un método dado.

METH_CLASS

  Al método se le pasará el objeto tipo como primer parámetro, en lugar de una instancia del tipo. Esto se utiliza para crear métodos de clase (class methods), similar a lo que se crea cuando se utiliza la función `classmethod()` incorporada.

METH_STATIC

  El método pasará `NULL` como el primer parámetro en lugar de una instancia del tipo. Esto se utiliza para crear métodos estáticos (static methods), similar a lo que se crea cuando se utiliza la función `staticmethod()` incorporada.

En otros controles constantes dependiendo si se carga un método en su lugar (in place) de otra definición con el mismo nombre del método.

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 *module, PyTypeObject *cls)
  Return value: New reference. Part of the Stable ABI 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 can be `NULL`.

  The callable object’s `__module__` attribute can be set from the given module argument. module 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`.

  Ver también

  `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 *module)
  Return value: New reference. Part of the Stable ABI.

  Equivalent to `PyCMethod_New(ml, self, module, NULL)`.

PyObject *PyCFunction_New(PyMethodDef *ml, PyObject *self)
  Return value: New reference. Part of the Stable ABI since version 3.4.

  Equivalent to `PyCMethod_New(ml, self, NULL, NULL)`.

## Acceder a atributos de tipos de extensión

type PyMemberDef
  Part of the Stable ABI (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` slot.

  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`, for example:

      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` instead.

  Distinto en la versión 3.12: `PyMemberDef` is always available. Previously, it required including `"structmember.h"`.

PyObject *PyMember_GetOne(const char *obj_addr, struct PyMemberDef *m)
  Part of the Stable ABI.

  Obtiene un atributo que pertenece al objeto en la dirección obj_addr. El atributo se describe por `PyMemberDef` m. Retorna `NULL` en caso de error.

  Distinto en la versión 3.12: `PyMember_GetOne` is always available. Previously, it required including `"structmember.h"`.

int PyMember_SetOne(char *obj_addr, struct PyMemberDef *m, PyObject *o)
  Part of the Stable ABI.

  Establece un atributo que pertenece al objeto en la dirección obj_addr al objeto o. El atributo a establecer se describe por `PyMemberDef` m. Retorna `0` si tiene éxito y un valor negativo si falla.

  Distinto en la versión 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.

Distinto en la versión 3.10: The `RESTRICTED`, `READ_RESTRICTED` and `WRITE_RESTRICTED` macros available with `#include "structmember.h"` are deprecated. `READ_RESTRICTED` and `RESTRICTED` are equivalent to `Py_AUDIT_READ`; `WRITE_RESTRICTED` does nothing.

Distinto en la versión 3.12: The `READONLY` macro was renamed to `Py_READONLY`. The `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` is raised.

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

Nombre de la macro | Tipo C | Python type
--- | --- | ---
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

  Like `Py_T_OBJECT_EX`, but `NULL` is converted to `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
  Part of the Stable ABI (including all members).

  Estructura para definir el acceso para un tipo como el de una propiedad. Véase también la descripción de la ranura `PyTypeObject.tp_getset`.

  const char *name

    nombre del atributo

  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

    docstring opcional

  void *closure

    Optional user data pointer, providing additional data for getter and setter.

typedef PyObject *(*getter)(PyObject*, void*)
  Part of the Stable ABI.

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

  Debe retornar una nueva referencia en caso de éxito o `NULL` con una excepción establecida en caso de error.

typedef int (*setter)(PyObject*, PyObject*, void*)
  Part of the Stable ABI.

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

  En caso de que el atributo deba suprimirse el segundo parámetro es `NULL`. Debe retornar `0` en caso de éxito o `-1` con una excepción explícita en caso de fallo.