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103
Doc/c-api/structures.rst
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@ -9,28 +9,29 @@ There are a large number of structures which are used in the definition of
object types for Python. This section describes these structures and how they
are used.
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
:ctype:`PyObject` and :ctype:`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.
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
:ctype:`PyObject` and :ctype:`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.
.. ctype:: 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. It corresponds to the fields defined
by the expansion of the ``PyObject_HEAD`` macro.
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. It
corresponds to the fields defined by the expansion of the ``PyObject_HEAD``
macro.
.. ctype:: PyVarObject
This is an extension of :ctype:`PyObject` that adds the :attr:`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. It corresponds to the fields defined by
the expansion of the ``PyObject_VAR_HEAD`` macro.
This is an extension of :ctype:`PyObject` that adds the :attr:`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. It corresponds to the
fields defined by the expansion of the ``PyObject_VAR_HEAD`` macro.
These macros are used in the definition of :ctype:`PyObject` and
:ctype:`PyVarObject`:
@ -41,9 +42,9 @@ These macros are used in the definition of :ctype:`PyObject` and
This is a macro which expands to the declarations of the fields of the
:ctype:`PyObject` type; it is used when declaring new types which represent
objects without a varying length. The specific fields it expands to depend on
the definition of :cmacro:`Py_TRACE_REFS`. By default, that macro is not
defined, and :cmacro:`PyObject_HEAD` expands to::
objects without a varying length. The specific fields it expands to depend
on the definition of :cmacro:`Py_TRACE_REFS`. By default, that macro is
not defined, and :cmacro:`PyObject_HEAD` expands to::
Py_ssize_t ob_refcnt;
PyTypeObject *ob_type;
@ -58,9 +59,9 @@ These macros are used in the definition of :ctype:`PyObject` and
.. cmacro:: PyObject_VAR_HEAD
This is a macro which expands to the declarations of the fields of the
:ctype:`PyVarObject` type; it is used when declaring new types which represent
objects with a length that varies from instance to instance. This macro always
expands to::
:ctype:`PyVarObject` type; it is used when declaring new types which
represent objects with a length that varies from instance to instance.
This macro always expands to::
PyObject_HEAD
Py_ssize_t ob_size;
@ -73,11 +74,12 @@ These macros are used in the definition of :ctype:`PyObject` and
.. ctype:: PyCFunction
Type of the functions used to implement most Python callables in C. Functions of
this type take two :ctype:`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.
Type of the functions used to implement most Python callables in C.
Functions of this type take two :ctype:`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.
.. ctype:: PyCFunctionWithKeywords
@ -126,20 +128,21 @@ convention flags can be combined with a binding flag.
.. data:: METH_VARARGS
This is the typical calling convention, where the methods have the type
:ctype:`PyCFunction`. The function expects two :ctype:`PyObject\*` values. The
first one is the *self* object for methods; for module functions, it has the
value given to :cfunc:`Py_InitModule4` (or *NULL* if :cfunc:`Py_InitModule` was
used). The second parameter (often called *args*) is a tuple object
representing all arguments. This parameter is typically processed using
:cfunc:`PyArg_ParseTuple` or :cfunc:`PyArg_UnpackTuple`.
:ctype:`PyCFunction`. The function expects two :ctype:`PyObject\*` values.
The first one is the *self* object for methods; for module functions, it
has the value given to :cfunc:`Py_InitModule4` (or *NULL* if
:cfunc:`Py_InitModule` was used). The second parameter (often called
*args*) is a tuple object representing all arguments. This parameter is
typically processed using :cfunc:`PyArg_ParseTuple` or
:cfunc:`PyArg_UnpackTuple`.
.. data:: METH_KEYWORDS
Methods with these flags must be of type :ctype:`PyCFunctionWithKeywords`. The
function expects three parameters: *self*, *args*, and a dictionary of all the
keyword arguments. The flag is typically combined with :const:`METH_VARARGS`,
and the parameters are typically processed using
Methods with these flags must be of type :ctype:`PyCFunctionWithKeywords`.
The function expects three parameters: *self*, *args*, and a dictionary of
all the keyword arguments. The flag is typically combined with
:const:`METH_VARARGS`, and the parameters are typically processed using
:cfunc:`PyArg_ParseTupleAndKeywords`.
@ -148,8 +151,8 @@ convention flags can be combined with a binding flag.
Methods without parameters don't need to check whether arguments are given if
they are listed with the :const:`METH_NOARGS` flag. They need to be of type
:ctype:`PyCFunction`. When used with object methods, the first parameter is
typically named ``self`` and will hold a reference to the object instance. In
all cases the second parameter will be *NULL*.
typically named ``self`` and will hold a reference to the object instance.
In all cases the second parameter will be *NULL*.
.. data:: METH_O
@ -170,18 +173,19 @@ method.
.. index:: builtin: classmethod
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 :func:`classmethod` built-in function.
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 :func:`classmethod` built-in
function.
.. data:: METH_STATIC
.. index:: builtin: staticmethod
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 :func:`staticmethod` built-in function.
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 :func:`staticmethod` built-in function.
One other constant controls whether a method is loaded in place of another
definition with the same method name.
@ -191,12 +195,13 @@ definition with the same method name.
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 :meth:`__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.
wrappers are loaded before the method table, the existence of a
*sq_contains* slot, for example, would generate a wrapped method named
:meth:`__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.
.. ctype:: PyMemberDef