List Objects

.. highlight:: c

.. _listobjects:

.. index:: pair: object; list

.. c:type:: PyListObject

This subtype of :c:type:PyObject represents a Python list object.

.. c:var:: PyTypeObject PyList_Type

This instance of :c:type:PyTypeObject represents the Python list type. This is the same object as :class:list in the Python layer.

.. c:function:: int PyList_Check(PyObject *p)

Return true if p is a list object or an instance of a subtype of the list type. This function always succeeds.

.. c:function:: int PyList_CheckExact(PyObject *p)

Return true if p is a list object, but not an instance of a subtype of the list type. This function always succeeds.

.. c:function:: PyObject* PyList_New(Py_ssize_t len)

Return a new list of length len on success, or NULL on failure.

.. note::

  If *len* is greater than zero, the returned list object's items are
  set to ``NULL``. Thus you cannot use abstract API functions such as
  :c:func:`PySequence_SetItem` or expose the object to Python code before
  setting all items to a real object with :c:func:`PyList_SetItem` or
  :c:func:`PyList_SET_ITEM()`. The following APIs are safe APIs before
  the list is fully initialized: :c:func:`PyList_SetItem()` and :c:func:`PyList_SET_ITEM()`.

.. c:function:: Py_ssize_t PyList_Size(PyObject *list)

.. index:: pair: built-in function; len

Return the length of the list object in list; this is equivalent to len(list) on a list object.

.. c:function:: Py_ssize_t PyList_GET_SIZE(PyObject *list)

Similar to :c:func:PyList_Size, but without error checking.

.. c:function:: PyObject* PyList_GetItemRef(PyObject *list, Py_ssize_t index)

Return the object at position index in the list pointed to by list. The position must be non-negative; indexing from the end of the list is not supported. If index is out of bounds (:code:<0 or >=len(list)), return NULL and set an :exc:IndexError exception.

.. versionadded:: 3.13

.. c:function:: PyObject* PyList_GetItem(PyObject *list, Py_ssize_t index)

Like :c:func:PyList_GetItemRef, but returns a :term:borrowed reference instead of a :term:strong reference.

.. note::

  In the :term:`free-threaded build`, the returned
  :term:`borrowed reference` may become invalid if another thread modifies
  the list concurrently. Prefer :c:func:`PyList_GetItemRef`, which returns
  a :term:`strong reference`.

.. c:function:: PyObject* PyList_GET_ITEM(PyObject *list, Py_ssize_t i)

Similar to :c:func:PyList_GetItem, but without error checking.

.. note::

  In the :term:`free-threaded build`, the returned
  :term:`borrowed reference` may become invalid if another thread modifies
  the list concurrently. Prefer :c:func:`PyList_GetItemRef`, which returns
  a :term:`strong reference`.

.. c:function:: int PyList_SetItem(PyObject *list, Py_ssize_t index, PyObject *item)

Set the item at index index in list to item. Return 0 on success. If index is out of bounds, return -1 and set an :exc:IndexError exception.

.. note::

  This function "steals" a reference to *item* and discards a reference to
  an item already in the list at the affected position.

.. c:function:: void PyList_SET_ITEM(PyObject *list, Py_ssize_t i, PyObject *o)

Macro form of :c:func:PyList_SetItem without error checking. This is normally only used to fill in new lists where there is no previous content.

Bounds checking is performed as an assertion if Python is built in :ref:debug mode <debug-build> or :option:with assertions <--with-assertions>.

.. note::

  This macro "steals" a reference to *item*, and, unlike
  :c:func:`PyList_SetItem`, does *not* discard a reference to any item that
  is being replaced; any reference in *list* at position *i* will be
  leaked.

.. note::

  In the :term:`free-threaded build`, this macro has no internal
  synchronization. It is normally only used to fill in new lists where no
  other thread has a reference to the list. If the list may be shared,
  use :c:func:`PyList_SetItem` instead, which uses a :term:`per-object
  lock`.

.. c:function:: int PyList_Insert(PyObject *list, Py_ssize_t index, PyObject *item)

Insert the item item into list list in front of index index. Return 0 if successful; return -1 and set an exception if unsuccessful. Analogous to list.insert(index, item).

.. c:function:: int PyList_Append(PyObject *list, PyObject *item)

Append the object item at the end of list list. Return 0 if successful; return -1 and set an exception if unsuccessful. Analogous to list.append(item).

.. c:function:: PyObject* PyList_GetSlice(PyObject *list, Py_ssize_t low, Py_ssize_t high)

Return a list of the objects in list containing the objects between low and high. Return NULL and set an exception if unsuccessful. Analogous to list[low:high]. Indexing from the end of the list is not supported.

.. c:function:: int PyList_SetSlice(PyObject *list, Py_ssize_t low, Py_ssize_t high, PyObject *itemlist)

Set the slice of list between low and high to the contents of itemlist. Analogous to list[low:high] = itemlist. The itemlist may be NULL, indicating the assignment of an empty list (slice deletion). Return 0 on success, -1 on failure. Indexing from the end of the list is not supported.

.. note::

  In the :term:`free-threaded build`, when *itemlist* is a :class:`list`,
  both *list* and *itemlist* are locked for the duration of the operation.
  For other iterables (or ``NULL``), only *list* is locked.

.. c:function:: int PyList_Extend(PyObject *list, PyObject *iterable)

Extend list with the contents of iterable. This is the same as PyList_SetSlice(list, PY_SSIZE_T_MAX, PY_SSIZE_T_MAX, iterable) and analogous to list.extend(iterable) or list += iterable.

Raise an exception and return -1 if list is not a :class:list object. Return 0 on success.

.. versionadded:: 3.13

.. note::

  In the :term:`free-threaded build`, when *iterable* is a :class:`list`,
  :class:`set`, :class:`dict`, or dict view, both *list* and *iterable*
  (or its underlying dict) are locked for the duration of the operation.
  For other iterables, only *list* is locked; *iterable* may be
  concurrently modified by another thread.

.. c:function:: int PyList_Clear(PyObject *list)

Remove all items from list. This is the same as PyList_SetSlice(list, 0, PY_SSIZE_T_MAX, NULL) and analogous to list.clear() or del list[:].

Raise an exception and return -1 if list is not a :class:list object. Return 0 on success.

.. versionadded:: 3.13

.. c:function:: int PyList_Sort(PyObject *list)

Sort the items of list in place. Return 0 on success, -1 on failure. This is equivalent to list.sort().

.. note::

  In the :term:`free-threaded build`, element comparison via
  :meth:`~object.__lt__` can execute arbitrary Python code, during which
  the :term:`per-object lock` may be temporarily released. For built-in
  types (:class:`str`, :class:`int`, :class:`float`), the lock is not
  released during comparison.

.. c:function:: int PyList_Reverse(PyObject *list)

Reverse the items of list in place. Return 0 on success, -1 on failure. This is the equivalent of list.reverse().

.. c:function:: PyObject* PyList_AsTuple(PyObject *list)

.. index:: pair: built-in function; tuple

Return a new tuple object containing the contents of list; equivalent to tuple(list).