Reference Counting

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

Py_ssize_t Py_REFCNT(PyObject *o)

Get the reference count of the Python object o.

Note that the returned value may not actually reflect how many references to the object are actually held. For example, some objects are immortal and have a very high refcount that does not reflect the actual number of references. Consequently, do not rely on the returned value to be accurate, other than a value of 0 or 1.

Use the Py_SET_REFCNT() function to set an object reference count.

Modifié dans la version 3.11: The parameter type is no longer const PyObject*.

Modifié dans la version 3.10: Py_REFCNT() is changed to the inline static function.

void Py_SET_REFCNT(PyObject *o, Py_ssize_t refcnt)

Set the object o reference counter to refcnt.

On Python build with Free Threading, if refcnt is larger than UINT32_MAX, the object is made immortal.

This function has no effect on immortal objects.

Nouveau dans la version 3.9.

Modifié dans la version 3.12: Immortal objects are not modified.

void Py_INCREF(PyObject *o)

Indicate taking a new strong reference to object o, indicating it is in use and should not be destroyed.

This function has no effect on immortal objects.

Cette fonction est souvent utilisée pour convertir une référence empruntée en une référence forte sur place. La fonction Py_NewRef() peut être utilisée pour créer une nouvelle référence forte.

When done using the object, release is by calling Py_DECREF().

L'objet ne doit pas être NULL, la fonction Py_XINCREF() doit être utilisée s'il est possible qu'il soit NULL.

Do not expect this function to actually modify o in any way. For at least some objects, this function has no effect.

Modifié dans la version 3.12: Immortal objects are not modified.

void Py_XINCREF(PyObject *o)

Similar to Py_INCREF(), but the object o can be NULL, in which case this has no effect.

Voir aussi Py_XNewRef().

PyObject *Py_NewRef(PyObject *o)
Part of the Stable ABI since version 3.10.

Create a new strong reference to an object: call Py_INCREF() on o and return the object o.

When the strong reference is no longer needed, Py_DECREF() should be called on it to release the reference.

L'objet o ne doit pas être NULL et la fonction Py_XNewRef() doit être utilisée si o peut être NULL.

Par exemple :

Py_INCREF(obj);
self->attr = obj;

peut s'écrire :

self->attr = Py_NewRef(obj);

Voir aussi Py_INCREF().

Nouveau dans la version 3.10.

PyObject *Py_XNewRef(PyObject *o)
Part of the Stable ABI since version 3.10.

Semblable à Py_NewRef() mais l'objet o peut être NULL.

Cette fonction renvoie NULL si l'objet o est NULL.

Nouveau dans la version 3.10.

void Py_DECREF(PyObject *o)

Release a strong reference to object o, indicating the reference is no longer used.

This function has no effect on immortal objects.

Once the last strong reference is released (i.e. the object's reference count reaches 0), the object's type's deallocation function (which must not be NULL) is invoked.

Cette fonction est généralement utilisée pour supprimer une référence forte avant qu'elle ne soit plus accessible.

L'objet en argument ne doit pas être NULL. Py_XDECREF() doit être utilisée si l'objet peut être NULL.

Do not expect this function to actually modify o in any way. For at least some objects, this function has no effect.

Avertissement

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.

Modifié dans la version 3.12: Immortal objects are not modified.

void Py_XDECREF(PyObject *o)

Similar to Py_DECREF(), but the object o can be NULL, in which case this has no effect. The same warning from Py_DECREF() applies here as well.

void Py_CLEAR(PyObject *o)

Release a strong reference 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 releasing the reference.

It is a good idea to use this macro whenever releasing a reference to an object that might be traversed during garbage collection.

Modifié dans la version 3.12: The macro argument is now only evaluated once. If the argument has side effects, these are no longer duplicated.

void Py_IncRef(PyObject *o)
Part of the Stable ABI.

Indicate taking a new strong reference to object o. A function version of Py_XINCREF(). It can be used for runtime dynamic embedding of Python.

void Py_DecRef(PyObject *o)
Part of the Stable ABI.

Release a strong reference to object o. A function version of Py_XDECREF(). It can be used for runtime dynamic embedding of Python.

Py_SETREF(dst, src)

Macro safely releasing a strong reference to object dst and setting dst to src.

As in case of Py_CLEAR(), "the obvious" code can be deadly:

Py_DECREF(dst);
dst = src;

The safe way is:

Py_SETREF(dst, src);

That arranges to set dst to src _before_ releasing the reference to the old value of dst, so that any code triggered as a side-effect of dst getting torn down no longer believes dst points to a valid object.

Nouveau dans la version 3.6.

Modifié dans la version 3.12: The macro arguments are now only evaluated once. If an argument has side effects, these are no longer duplicated.

Py_XSETREF(dst, src)

Variant of Py_SETREF macro that uses Py_XDECREF() instead of Py_DECREF().

Nouveau dans la version 3.6.

Modifié dans la version 3.12: The macro arguments are now only evaluated once. If an argument has side effects, these are no longer duplicated.