cpython/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)


.. 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; the *methods* argument can be *NULL* if no methods are
   to be defined for the module.


.. 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.  The *methods* argument can be *NULL* if no methods
   are to be defined for the module.  If *doc* is non-*NULL*, it will be used to
   define the docstring for the module.


.. 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.  The *methods* argument can be *NULL* if no methods
   are to be defined for the module.  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.


.. cvar:: PyObject _Py_NoneStruct

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