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ad0f618ab3
* Update documentation for tp_basicsize & tp_itemsize - Add alignment requirement - Mention that ob_size is unreliable if you don't control it - Add some links for context - basicsize should include the base type in generaly not just PyObject This adds a “by-the-way” link to `PyObject_New`, which shouldn't be used for GC types. In order to be comfortable linking to it, I also add a link to `PyObject_GC_New` from its docs. And the same for `*Var` variants, while I'm here. * Strongly suggest Py_SIZE & Py_SET_SIZE
76 lines
2.5 KiB
ReStructuredText
76 lines
2.5 KiB
ReStructuredText
.. highlight:: c
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.. _allocating-objects:
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Allocating Objects on the Heap
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==============================
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.. c:function:: PyObject* _PyObject_New(PyTypeObject *type)
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.. c:function:: PyVarObject* _PyObject_NewVar(PyTypeObject *type, Py_ssize_t size)
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.. c:function:: PyObject* PyObject_Init(PyObject *op, PyTypeObject *type)
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Initialize a newly allocated object *op* with its type and initial
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reference. Returns the initialized object. Other fields of the object are
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not affected.
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.. c:function:: PyVarObject* PyObject_InitVar(PyVarObject *op, PyTypeObject *type, Py_ssize_t size)
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This does everything :c:func:`PyObject_Init` does, and also initializes the
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length information for a variable-size object.
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.. c:macro:: PyObject_New(TYPE, typeobj)
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Allocate a new Python object using the C structure type *TYPE*
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and the Python type object *typeobj* (``PyTypeObject*``).
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Fields not defined by the Python object header are not initialized.
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The caller will own the only reference to the object
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(i.e. its reference count will be one).
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The size of the memory allocation is determined from the
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:c:member:`~PyTypeObject.tp_basicsize` field of the type object.
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Note that this function is unsuitable if *typeobj* has
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:c:macro:`Py_TPFLAGS_HAVE_GC` set. For such objects,
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use :c:func:`PyObject_GC_New` instead.
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.. c:macro:: PyObject_NewVar(TYPE, typeobj, size)
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Allocate a new Python object using the C structure type *TYPE* and the
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Python type object *typeobj* (``PyTypeObject*``).
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Fields not defined by the Python object header
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are not initialized. The allocated memory allows for the *TYPE* structure
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plus *size* (``Py_ssize_t``) fields of the size
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given by the :c:member:`~PyTypeObject.tp_itemsize` field of
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*typeobj*. This is useful for implementing objects like tuples, which are
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able to determine their size at construction time. Embedding the array of
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fields into the same allocation decreases the number of allocations,
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improving the memory management efficiency.
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Note that this function is unsuitable if *typeobj* has
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:c:macro:`Py_TPFLAGS_HAVE_GC` set. For such objects,
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use :c:func:`PyObject_GC_NewVar` instead.
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.. c:function:: void PyObject_Del(void *op)
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Same as :c:func:`PyObject_Free`.
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.. c:var:: PyObject _Py_NoneStruct
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Object which is visible in Python as ``None``. This should only be accessed
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using the :c:macro:`Py_None` macro, which evaluates to a pointer to this
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object.
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.. seealso::
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:c:func:`PyModule_Create`
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To allocate and create extension modules.
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