cpython/Include/listobject.h

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/* List object interface */
/*
Another generally useful object type is an list of object pointers.
This is a mutable type: the list items can be changed, and items can be
added or removed. Out-of-range indices or non-list objects are ignored.
*** WARNING *** PyList_SetItem does not increment the new item's reference
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count, but does decrement the reference count of the item it replaces,
if not nil. It does *decrement* the reference count if it is *not*
inserted in the list. Similarly, PyList_GetItem does not increment the
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returned item's reference count.
*/
#ifndef Py_LISTOBJECT_H
#define Py_LISTOBJECT_H
#ifdef __cplusplus
extern "C" {
#endif
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typedef struct {
PyObject_VAR_HEAD
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/* Vector of pointers to list elements. list[0] is ob_item[0], etc. */
PyObject **ob_item;
/* ob_item contains space for 'allocated' elements. The number
* currently in use is ob_size.
* Invariants:
* 0 <= ob_size <= allocated
* len(list) == ob_size
* ob_item == NULL implies ob_size == allocated == 0
* list.sort() temporarily sets allocated to -1 to detect mutations.
*
* Items must normally not be NULL, except during construction when
* the list is not yet visible outside the function that builds it.
*/
* Optimized list appends and pops by making fewer calls the underlying system realloc(). This is achieved by tracking the overallocation size in a new field and using that information to skip calls to realloc() whenever possible. * Simplified and tightened the amount of overallocation. For larger lists, this overallocates by 1/8th (compared to the previous scheme which ranged between 1/4th to 1/32nd over-allocation). For smaller lists (n<6), the maximum overallocation is one byte (formerly it could be upto eight bytes). This saves memory in applications with large numbers of small lists. * Eliminated the NRESIZE macro in favor of a new, static list_resize function that encapsulates the resizing logic. Coverting this back to macro would give a small (under 1%) speed-up. This was too small to warrant the loss of readability, maintainability, and de-coupling. * Some functions using NRESIZE had grown unnecessarily complex in their efforts to bend to the macro's calling pattern. With the new list_resize function in place, those other functions could be simplified. That is being saved for a separate patch. * The ob_item==NULL check could be eliminated from the new list_resize function. This would entail finding each piece of code that sets ob_item to NULL and adding a new line to invalidate the overallocation tracking field. Rather than impose a new requirement on other pieces of list code, it was preferred to leave the NULL check in place and retain the benefits of decoupling, maintainability and information hiding (only PyList_New() and list_sort() need to know about the new field). This approach also reduces the odds of breaking an extension module. (Collaborative effort by Raymond Hettinger, Hye-Shik Chang, Tim Peters, and Armin Rigo.)
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int allocated;
} PyListObject;
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PyAPI_DATA(PyTypeObject) PyList_Type;
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#define PyList_Check(op) PyObject_TypeCheck(op, &PyList_Type)
#define PyList_CheckExact(op) ((op)->ob_type == &PyList_Type)
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PyAPI_FUNC(PyObject *) PyList_New(int size);
PyAPI_FUNC(int) PyList_Size(PyObject *);
PyAPI_FUNC(PyObject *) PyList_GetItem(PyObject *, int);
PyAPI_FUNC(int) PyList_SetItem(PyObject *, int, PyObject *);
PyAPI_FUNC(int) PyList_Insert(PyObject *, int, PyObject *);
PyAPI_FUNC(int) PyList_Append(PyObject *, PyObject *);
PyAPI_FUNC(PyObject *) PyList_GetSlice(PyObject *, int, int);
PyAPI_FUNC(int) PyList_SetSlice(PyObject *, int, int, PyObject *);
PyAPI_FUNC(int) PyList_Sort(PyObject *);
PyAPI_FUNC(int) PyList_Reverse(PyObject *);
PyAPI_FUNC(PyObject *) PyList_AsTuple(PyObject *);
PyAPI_FUNC(PyObject *) _PyList_Extend(PyListObject *, PyObject *);
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/* Macro, trading safety for speed */
#define PyList_GET_ITEM(op, i) (((PyListObject *)(op))->ob_item[i])
#define PyList_SET_ITEM(op, i, v) (((PyListObject *)(op))->ob_item[i] = (v))
#define PyList_GET_SIZE(op) (((PyListObject *)(op))->ob_size)
#ifdef __cplusplus
}
#endif
#endif /* !Py_LISTOBJECT_H */