symbian-qemu-0.9.1-12/python-2.6.1/Doc/c-api/cell.rst
author andy simpson <andrews@symbian.org>
Fri, 08 Oct 2010 16:52:59 +0100
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permissions -rw-r--r--
work-a-round for Bug 3645 change ARGB->XRGB pixel format
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.. highlightlang:: c
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.. _cell-objects:
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Cell Objects
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------------
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"Cell" objects are used to implement variables referenced by multiple scopes.
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For each such variable, a cell object is created to store the value; the local
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variables of each stack frame that references the value contains a reference to
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the cells from outer scopes which also use that variable.  When the value is
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accessed, the value contained in the cell is used instead of the cell object
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itself.  This de-referencing of the cell object requires support from the
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generated byte-code; these are not automatically de-referenced when accessed.
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Cell objects are not likely to be useful elsewhere.
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.. ctype:: PyCellObject
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   The C structure used for cell objects.
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.. cvar:: PyTypeObject PyCell_Type
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   The type object corresponding to cell objects.
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.. cfunction:: int PyCell_Check(ob)
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   Return true if *ob* is a cell object; *ob* must not be *NULL*.
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.. cfunction:: PyObject* PyCell_New(PyObject *ob)
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   Create and return a new cell object containing the value *ob*. The parameter may
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   be *NULL*.
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.. cfunction:: PyObject* PyCell_Get(PyObject *cell)
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   Return the contents of the cell *cell*.
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.. cfunction:: PyObject* PyCell_GET(PyObject *cell)
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   Return the contents of the cell *cell*, but without checking that *cell* is
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   non-*NULL* and a cell object.
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.. cfunction:: int PyCell_Set(PyObject *cell, PyObject *value)
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   Set the contents of the cell object *cell* to *value*.  This releases the
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   reference to any current content of the cell. *value* may be *NULL*.  *cell*
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   must be non-*NULL*; if it is not a cell object, ``-1`` will be returned.  On
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   success, ``0`` will be returned.
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.. cfunction:: void PyCell_SET(PyObject *cell, PyObject *value)
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   Sets the value of the cell object *cell* to *value*.  No reference counts are
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   adjusted, and no checks are made for safety; *cell* must be non-*NULL* and must
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   be a cell object.