Doc/c-api/allocation.rst

.. highlightlang:: c

.. _allocating-objects:

Allocating Objects on the Heap
==============================


.. cfunction:: PyObject* _PyObject_New(PyTypeObject *type)


.. cfunction:: PyVarObject* _PyObject_NewVar(PyTypeObject *type, Py_ssize_t size)

   .. versionchanged:: 2.5
      This function used an :ctype:`int` type for *size*. This might require
      changes in your code for properly supporting 64-bit systems.


.. cfunction:: void _PyObject_Del(PyObject *op)


.. cfunction:: PyObject* PyObject_Init(PyObject *op, PyTypeObject *type)

   Initialize a newly-allocated object *op* with its type and initial reference.
   Returns the initialized object.  If *type* indicates that the object
   participates in the cyclic garbage detector, it is added to the detector's set
   of observed objects. Other fields of the object are not affected.


.. cfunction:: PyVarObject* PyObject_InitVar(PyVarObject *op, PyTypeObject *type, Py_ssize_t size)

   This does everything :cfunc:`PyObject_Init` does, and also initializes the
   length information for a variable-size object.


.. cfunction:: TYPE* PyObject_New(TYPE, PyTypeObject *type)

   Allocate a new Python object using the C structure type *TYPE* and the Python
   type object *type*.  Fields not defined by the Python object header are not
   initialized; the object's reference count will be one.  The size of the memory
   allocation is determined from the :attr:`tp_basicsize` field of the type object.


.. cfunction:: TYPE* PyObject_NewVar(TYPE, PyTypeObject *type, Py_ssize_t size)

   Allocate a new Python object using the C structure type *TYPE* and the Python
   type object *type*.  Fields not defined by the Python object header are not
   initialized.  The allocated memory allows for the *TYPE* structure plus *size*
   fields of the size given by the :attr:`tp_itemsize` field of *type*.  This is
   useful for implementing objects like tuples, which are able to determine their
   size at construction time.  Embedding the array of fields into the same
   allocation decreases the number of allocations, improving the memory management
   efficiency.


.. cfunction:: void PyObject_Del(PyObject *op)

   Releases memory allocated to an object using :cfunc:`PyObject_New` or
   :cfunc:`PyObject_NewVar`.  This is normally called from the :attr:`tp_dealloc`
   handler specified in the object's type.  The fields of the object should not be
   accessed after this call as the memory is no longer a valid Python object.


.. cfunction:: PyObject* Py_InitModule(char *name, PyMethodDef *methods)

   Create a new module object based on a name and table of functions, returning the
   new module object.

   .. versionchanged:: 2.3
      Older versions of Python did not support *NULL* as the value for the *methods*
      argument.


.. cfunction:: PyObject* Py_InitModule3(char *name, PyMethodDef *methods, char *doc)

   Create a new module object based on a name and table of functions, returning the
   new module object.  If *doc* is non-*NULL*, it will be used to define the
   docstring for the module.

   .. versionchanged:: 2.3
      Older versions of Python did not support *NULL* as the value for the *methods*
      argument.


.. cfunction:: PyObject* Py_InitModule4(char *name, PyMethodDef *methods, char *doc, PyObject *self, int apiver)

   Create a new module object based on a name and table of functions, returning the
   new module object.  If *doc* is non-*NULL*, it will be used to define the
   docstring for the module.  If *self* is non-*NULL*, it will passed to the
   functions of the module as their (otherwise *NULL*) first parameter.  (This was
   added as an experimental feature, and there are no known uses in the current
   version of Python.)  For *apiver*, the only value which should be passed is
   defined by the constant :const:`PYTHON_API_VERSION`.

   .. note::

      Most uses of this function should probably be using the :cfunc:`Py_InitModule3`
      instead; only use this if you are sure you need it.

   .. versionchanged:: 2.3
      Older versions of Python did not support *NULL* as the value for the *methods*
      argument.


.. cvar:: PyObject _Py_NoneStruct

   Object which is visible in Python as ``None``.  This should only be accessed
   using the ``Py_None`` macro, which evaluates to a pointer to this object.