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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 beforePy_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 callPy_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 forPy_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
.