GNU Info

(python2.1-api.info)Reference Counting

---

Next: Exception Handling Prev: Very High Level Layer Up: Top

---

Enter node , (file) or (file)node

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.

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'.