
Reference Counting
******************

The macros in this section are used for managing reference counts of
Python objects.

void Py_INCREF(PyObject *o)

   Increment the reference count for object *o*.  The object must not
   be *NULL*; if you aren't sure that it isn't *NULL*, use
   ``Py_XINCREF()``.

void Py_XINCREF(PyObject *o)

   Increment the reference count for object *o*.  The object may be
   *NULL*, in which case the macro has no effect.

void Py_DECREF(PyObject *o)

   Decrement the reference count for object *o*.  The object must not
   be *NULL*; if you aren't sure that it isn't *NULL*, use
   ``Py_XDECREF()``.  If the reference count reaches zero, the
   object's type's deallocation function (which must not be *NULL*) is
   invoked.

   Warning: The deallocation function can cause arbitrary Python code to be
     invoked (e.g. when a class instance with a ``__del__()`` method
     is deallocated).  While exceptions in such code are not
     propagated, the executed code has free access to all Python
     global variables.  This means that any object that is reachable
     from a global variable should be in a consistent state before
     ``Py_DECREF()`` is invoked.  For example, code to delete an
     object from a list should copy a reference to the deleted object
     in a temporary variable, update the list data structure, and then
     call ``Py_DECREF()`` for the temporary variable.

void Py_XDECREF(PyObject *o)

   Decrement the reference count for object *o*.  The object may be
   *NULL*, in which case the macro has no effect; otherwise the effect
   is the same as for ``Py_DECREF()``, and the same warning applies.

void Py_CLEAR(PyObject *o)

   Decrement the reference count for object *o*.  The object may be
   *NULL*, in which case the macro has no effect; otherwise the effect
   is the same as for ``Py_DECREF()``, except that the argument is
   also set to *NULL*.  The warning for ``Py_DECREF()`` does not apply
   with respect to the object passed because the macro carefully uses
   a temporary variable and sets the argument to *NULL* before
   decrementing its reference count.

   It is a good idea to use this macro whenever decrementing the value
   of a variable that might be traversed during garbage collection.

   New in version 2.4.

The following functions are for runtime dynamic embedding of Python:
``Py_IncRef(PyObject *o)``, ``Py_DecRef(PyObject *o)``. They are
simply exported function versions of ``Py_XINCREF()`` and
``Py_XDECREF()``, respectively.

The following functions or macros are only for use within the
interpreter core: ``_Py_Dealloc()``, ``_Py_ForgetReference()``,
``_Py_NewReference()``, as well as the global variable
``_Py_RefTotal``.
