.. highlightlang:: c

.. _cell-objects:

Cell Objects

------------

"Cell" objects are used to implement variables referenced by multiple scopes.

For each such variable, a cell object is created to store the value; the local

variables of each stack frame that references the value contains a reference to

the cells from outer scopes which also use that variable.  When the value is

accessed, the value contained in the cell is used instead of the cell object

itself.  This de-referencing of the cell object requires support from the

generated byte-code; these are not automatically de-referenced when accessed.

Cell objects are not likely to be useful elsewhere.

.. ctype:: PyCellObject

   The C structure used for cell objects.

.. cvar:: PyTypeObject PyCell_Type

   The type object corresponding to cell objects.

.. cfunction:: int PyCell_Check(ob)

   Return true if *ob* is a cell object; *ob* must not be *NULL*.

.. cfunction:: PyObject* PyCell_New(PyObject *ob)

   Create and return a new cell object containing the value *ob*. The parameter may

   be *NULL*.

.. cfunction:: PyObject* PyCell_Get(PyObject *cell)

   Return the contents of the cell *cell*.

.. cfunction:: PyObject* PyCell_GET(PyObject *cell)

   Return the contents of the cell *cell*, but without checking that *cell* is

   non-*NULL* and a cell object.

.. cfunction:: int PyCell_Set(PyObject *cell, PyObject *value)

   Set the contents of the cell object *cell* to *value*.  This releases the

   reference to any current content of the cell. *value* may be *NULL*.  *cell*

   must be non-*NULL*; if it is not a cell object, ``-1`` will be returned.  On

   success, ``0`` will be returned.

.. cfunction:: void PyCell_SET(PyObject *cell, PyObject *value)

   Sets the value of the cell object *cell* to *value*.  No reference counts are

   adjusted, and no checks are made for safety; *cell* must be non-*NULL* and must

   be a cell object.