Cell 物件
*********

「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.

PyCellObject

   C 結構的 cell 物件

PyTypeObject PyCell_Type

   對應 cell 物件的物件型別。

int PyCell_Check(ob)

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

PyObject* PyCell_New(PyObject *ob)
    *Return value: New reference.*

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

PyObject* PyCell_Get(PyObject *cell)
    *Return value: New reference.*

   回傳 cell 內容中的 *cell*。

PyObject* PyCell_GET(PyObject *cell)
    *Return value: Borrowed reference.*

   Return the contents of the cell *cell*, but without checking that
   *cell* is non-*NULL* and a cell object.

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.

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.
