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authorGeorg Brandl <georg@python.org>2008-01-20 09:30:57 (GMT)
committerGeorg Brandl <georg@python.org>2008-01-20 09:30:57 (GMT)
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+.. 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.