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.
