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*.

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

   Changed in version 3.11: The parameter type is no longer const
   PyObject*.

   Changed in 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*.

   New in version 3.9.

void Py_INCREF(PyObject *o)

   Increment the reference count for object *o*.

   This function is usually used to convert a *borrowed reference* to
   a *strong reference* in-place. The "Py_NewRef()" function can be
   used to create a new *strong reference*.

   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.

   See also "Py_XNewRef()".

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

   Create a new *strong reference* to an object: increment the
   reference count of the object *o* and return the object *o*.

   When the *strong reference* is no longer needed, "Py_DECREF()"
   should be called on it to decrement the object reference count.

   The object *o* must not be "NULL"; use "Py_XNewRef()" if *o* can be
   "NULL".

   For example:

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

   can be written as:

      self->attr = Py_NewRef(obj);

   See also "Py_INCREF()".

   New in version 3.10.

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

   Similar to "Py_NewRef()", but the object *o* can be NULL.

   If the object *o* is "NULL", the function just returns "NULL".

   New in version 3.10.

void Py_DECREF(PyObject *o)

   Decrement the reference count for object *o*.

   If the reference count reaches zero, the object's type's
   deallocation function (which must not be "NULL") is invoked.

   This function is usually used to delete a *strong reference* before
   exiting its scope.

   The object must not be "NULL"; if you aren't sure that it isn't
   "NULL", use "Py_XDECREF()".

   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
   reference count of an object that might be traversed during garbage
   collection.

   Changed in 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.*

   Increment the reference count for 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.*

   Decrement the reference count for object *o*. A function version of
   "Py_XDECREF()". It can be used for runtime dynamic embedding of
   Python.

Py_SETREF(dst, src)

   Macro safely decrementing the *dst* reference count 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_ decrementing reference
   count of *dst* old value, so that any code triggered as a side-
   effect of *dst* getting torn down no longer believes *dst* points
   to a valid object.

   New in version 3.6.

   Changed in 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()".

   New in version 3.6.

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