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Python/C API Reference Manual |
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3. Reference Counting
The macros in this section are used for managing reference counts
of Python objects.
| void Py_INCREF( | PyObject *o) |
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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) |
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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.
Release 2.4.5, documentation updated on 18 October 2006.
See About this document... for information on suggesting changes.
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