Wspólne struktury obiektów
**************************

Istnieje duża liczba struktur, które są używane przy definiowaniu
rodzajów obiektów w Pythonie. Ten rozdział opisuje te struktury i jak
są one używane.


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.

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:

      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.

Py_TYPE(o)

   This macro is used to access the "ob_type" member of a Python
   object. It expands to:

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

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".

   Nowe w wersji 3.9.

void Py_SET_TYPE(PyObject *o, PyTypeObject *type)

   Set the object *o* type to *type*.

   Nowe w wersji 3.9.

Py_REFCNT(o)

   This macro is used to access the "ob_refcnt" member of a Python
   object. It expands to:

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

void Py_SET_REFCNT(PyObject *o, Py_ssize_t refcnt)

   Set the object *o* reference counter to *refcnt*.

   Nowe w wersji 3.9.

Py_SIZE(o)

   This macro is used to access the "ob_size" member of a Python
   object. It expands to:

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

void Py_SET_SIZE(PyVarObject *o, Py_ssize_t size)

   Set the object *o* size to *size*.

   Nowe w wersji 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
==================================

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.

   The function signature is:

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

PyCFunctionWithKeywords

   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);

_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);

_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);

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)

   Nowe w wersji 3.9.

PyMethodDef

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

   +--------------------+-----------------+---------------------------------+
   | Field              | typ języka C    | Znaczenie                       |
   |====================|=================|=================================|
   | "ml_name"          | const char *    | name of the method              |
   +--------------------+-----------------+---------------------------------+
   | "ml_meth"          | PyCFunction     | pointer to the C implementation |
   +--------------------+-----------------+---------------------------------+
   | "ml_flags"         | int             | 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 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_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.

   Nowe w wersji 3.7.

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.

   This is not part of the limited API.

   Nowe w wersji 3.7.

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".

   Nowe w wersji 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".

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.

Te dwie stałe nie są używane do zaznaczania konwencji wywoływania, ale
wiążą gdy są używane z metodami klas. Nie mogą być one używane dla
funkcji określonych dla modułów. Co najwyżej jedna z tych flag może
być ustawiona dla dowolnej danej metody.

METH_CLASS

   Metodzie zostanie przekazany typ obiektu jako pierwszy parametr
   zamiast instancji tego typu. Jest to używane aby tworzyć *metody
   klasowe*, podobnie do tego, co jest tworzone przy użyciu wbudowanej
   funkcji "classmethod()".

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.

Jedna pozostała stała kontroluje czy metoda jest ładowana w miejscu
innej definicji o tej samej nazwie metody.

METH_COEXIST

   Metoda zostanie załadowana w miejsce istniejących definicji. Bez
   *METH_COEXIST*, domyślnie pomija się powtórzone definicje. Od kiedy
   opakowania gniazd są ładowane przed tabelą metod, istnienie na
   przykład gniazda *sq_contains* generuje opakowaną metodę nazywaną
   "__contains__()" i zapobiega ładowaniu odpowiadającej funkcji
   PyCFunction o tej samej nazwie. Ze zdefiniowaną flagą, PyCFunction
   zostanie załadowana w miejsce obiektu opakowania i będzie
   współistniała z gniazdem. To jest pomocne ponieważ wywołania
   PyCFunction są zoptymalizowane bardziej niż odwołania do obiektów
   opakowań.


Accessing attributes of extension types
=======================================

PyMemberDef

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

   +--------------------+-----------------+---------------------------------+
   | Field              | typ języka C    | Znaczenie                       |
   |====================|=================|=================================|
   | "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      | C type             |
   |=================|====================|
   | T_SHORT         | short              |
   +-----------------+--------------------+
   | T_INT           | int                |
   +-----------------+--------------------+
   | T_LONG          | long               |
   +-----------------+--------------------+
   | T_FLOAT         | typ (float)        |
   |                 | zmiennoprzecinkowy |
   |                 | pojedynczej        |
   |                 | precyzji           |
   +-----------------+--------------------+
   | T_DOUBLE        | typ (double)       |
   |                 | zmiennoprzecinkowy |
   |                 | podwójnej precyzji |
   +-----------------+--------------------+
   | T_STRING        | const char *       |
   +-----------------+--------------------+
   | T_OBJECT        | PyObject *         |
   +-----------------+--------------------+
   | T_OBJECT_EX     | PyObject *         |
   +-----------------+--------------------+
   | T_CHAR          | char               |
   +-----------------+--------------------+
   | T_BYTE          | char               |
   +-----------------+--------------------+
   | T_UBYTE         | nieoznaczony typ   |
   |                 | znakowy            |
   +-----------------+--------------------+
   | T_UINT          | nieoznaczony typ   |
   |                 | int                |
   +-----------------+--------------------+
   | T_USHORT        | nieoznaczony typ   |
   |                 | krótki             |
   +-----------------+--------------------+
   | T_ULONG         | nieoznaczony typ   |
   |                 | długi              |
   +-----------------+--------------------+
   | 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.

PyGetSetDef

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

   +---------------+--------------------+-------------------------------------+
   | Field         | typ języka C       | Znaczenie                           |
   |===============|====================|=====================================|
   | name          | 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"):

      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 function 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.
