# Estruturas comuns de objetos

Existe um grande número de estruturas usadas para a definição de tipos objeto para o Python. Esta seção descreve essas estruturas e como são usadas.

## Base object types and 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.

type PyObject
  Parte da API Limitada. (Somente alguns membros são parte da ABI estável.)

  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
  Parte da API Limitada. (Somente alguns membros são parte da ABI estável.)

  Esta é uma extensão de `PyObject` que adiciona o campo `ob_size`. Isso é usado apenas para objetos que têm alguma noção de comprimento. Esse tipo não costuma aparecer na API Python/C. O acesso aos membros deve ser feito através das macros `Py_REFCNT`, `Py_TYPE`, e `Py_SIZE`.

PyObject_HEAD

  Este é um macro usado ao declarar novos tipos que representam objetos sem comprimento variável. O macro PyObject_HEAD se expande para:

      PyObject ob_base;

  Veja documentação de `PyObject` acima.

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;

  Veja documentação de `PyVarObject` acima.

int Py_Is(PyObject *x, PyObject *y)
  Parte da ABI Estável desde a versão 3.10.

  Testa se o objeto x é o objeto y, o mesmo que `x is y` em Python.

  Novo na versão 3.10.

int Py_IsNone(PyObject *x)
  Parte da ABI Estável desde a versão 3.10.

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

  Novo na versão 3.10.

int Py_IsTrue(PyObject *x)
  Parte da ABI Estável desde a versão 3.10.

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

  Novo na versão 3.10.

int Py_IsFalse(PyObject *x)
  Parte da ABI Estável desde a versão 3.10.

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

  Novo na versão 3.10.

PyTypeObject *Py_TYPE(PyObject *o)

  Get the type of the Python object o.

  Return a borrowed reference.

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

  Alterado na versão 3.11: `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 type is type. Return zero otherwise. Equivalent to: `Py_TYPE(o) == type`.

  Novo na versão 3.9.

void Py_SET_TYPE(PyObject *o, PyTypeObject *type)

  Set the object o type to type.

  Novo na versão 3.9.

Py_ssize_t Py_REFCNT(PyObject *o)

  Get the reference count of the Python object o.

  Use the `Py_SET_REFCNT()` function to set an object reference count.

  Alterado na versão 3.11: The parameter type is no longer const PyObject*.

  Alterado na versão 3.10: `Py_REFCNT()` is changed to the inline static function.

void Py_SET_REFCNT(PyObject *o, Py_ssize_t refcnt)

  Set the object o reference counter to refcnt.

  Novo na versão 3.9.

Py_ssize_t Py_SIZE(PyVarObject *o)

  Get the size of the Python object o.

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

  Alterado na versão 3.11: `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)

  Set the object o size to size.

  Novo na versão 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,

## Implementing functions and methods

type PyCFunction
  Parte da ABI Estável.

  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.

  A assinatura da função é:

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

type PyCFunctionWithKeywords
  Parte da ABI Estável.

  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)

  Novo na versão 3.9.

type PyMethodDef
  Parte da ABI Estável (incluindo todos os membros).

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

  const char *ml_name

    Nome do método.

  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.

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).

  Novo na versão 3.7.

  Alterado na versão 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.

  Novo na versão 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`.

  Novo na versão 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()` 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.

PyObject *PyCMethod_New(PyMethodDef *ml, PyObject *self, PyObject *module, PyTypeObject *cls)
  Retorna valor: Nova referência. Parte da ABI Estável desde a versão 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 também

  `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`.

  Novo na versão 3.9.

PyObject *PyCFunction_NewEx(PyMethodDef *ml, PyObject *self, PyObject *module)
  Retorna valor: Nova referência. Parte da ABI Estável.

  Equivalente a `PyCMethod_New(ml, self, module, NULL)`.

PyObject *PyCFunction_New(PyMethodDef *ml, PyObject *self)
  Retorna valor: Nova referência. Parte da ABI Estável desde a versão 3.4.

  Equivalente a `PyCMethod_New(ml, self, NULL, NULL)`.

## Accessing attributes of extension types

type PyMemberDef
  Parte da ABI Estável (incluindo todos os membros).

  Structure which describes an attribute of a type which corresponds to a C struct member. Its fields are:

  Campo | Tipo em C | Significado
  --- | --- | ---
  `name` | const char * | name of the member
  `type` | int | 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` | int | 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 | Tipo em C
  --- | ---
  T_SHORT | short
  T_INT | int
  T_LONG | long
  T_FLOAT | ponto flutuante
  T_DOUBLE | double
  T_STRING | const char *
  T_OBJECT | PyObject *
  T_OBJECT_EX | PyObject *
  T_CHAR | char
  T_BYTE | char
  T_UBYTE | unsigned char
  T_UINT | unsigned int
  T_USHORT | unsigned short
  T_ULONG | unsigned long
  T_BOOL | char
  T_LONGLONG | long long
  T_ULONGLONG | unsigned 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`).

  Heap allocated types (created using `PyType_FromSpec()` or similar), `PyMemberDef` may contain definitions for the special members `__dictoffset__`, `__weaklistoffset__` and `__vectorcalloffset__`, corresponding to `tp_dictoffset`, `tp_weaklistoffset` and `tp_vectorcall_offset` in type objects. These must be defined with `T_PYSSIZET` and `READONLY`, for example:

      static PyMemberDef spam_type_members[] = {
          {"__dictoffset__", T_PYSSIZET, offsetof(Spam_object, dict), READONLY},
          {NULL}  /* Sentinel */
      };

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

  Get an attribute belonging to the object at address obj_addr. The attribute is described by `PyMemberDef` m. Returns `NULL` on error.

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

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

type PyGetSetDef
  Parte da ABI Estável (incluindo todos os membros).

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

  Campo | Tipo em C | Significado
  --- | --- | ---
  nome | 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 user data pointer, providing additional data for getter and setter

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

      typedef PyObject *(*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 user data pointer (the associated `closure`):

      typedef int (*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.