.. highlight:: c

.. _tupleobjects:

Tuple Objects

-------------

.. index:: pair: object; tuple

.. c:type:: PyTupleObject

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

.. c:var:: PyTypeObject PyTuple_Type

This instance of :c:type:`PyTypeObject` represents the Python tuple type; it

is the same object as :class:`tuple` in the Python layer.

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

Return true if *p* is a tuple object or an instance of a subtype of the

tuple type. This function always succeeds.

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

Return true if *p* is a tuple object, but not an instance of a subtype of the

tuple type. This function always succeeds.

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

Return a new tuple object of size *len*,

or ``NULL`` with an exception set on failure.

.. c:function:: PyObject* PyTuple_FromArray(PyObject *const *array, Py_ssize_t size)

Create a tuple of *size* items and copy references from *array* to the new

tuple.

*array* can be NULL if *size* is ``0``.

On success, return a new reference.

On error, set an exception and return ``NULL``.

.. versionadded:: 3.15

.. c:function:: PyObject* PyTuple_Pack(Py_ssize_t n, ...)

Return a new tuple object of size *n*,

or ``NULL`` with an exception set on failure. The tuple values

are initialized to the subsequent *n* C arguments pointing to Python objects.

``PyTuple_Pack(2, a, b)`` is equivalent to ``Py_BuildValue("(OO)", a, b)``.

.. c:function:: Py_ssize_t PyTuple_Size(PyObject *p)

Take a pointer to a tuple object, and return the size of that tuple.

On error, return ``-1`` with an exception set.

.. c:function:: Py_ssize_t PyTuple_GET_SIZE(PyObject *p)

Like :c:func:`PyTuple_Size`, but without error checking.

.. c:function:: PyObject* PyTuple_GetItem(PyObject *p, Py_ssize_t pos)

Return the object at position *pos* in the tuple pointed to by *p*. If *pos* is

negative or out of bounds, return ``NULL`` and set an :exc:`IndexError` exception.

The returned reference is borrowed from the tuple *p*

(that is: it is only valid as long as you hold a reference to *p*).

To get a :term:`strong reference`, use

:c:func:`Py_NewRef(PyTuple_GetItem(...)) <Py_NewRef>`

or :c:func:`PySequence_GetItem`.

.. c:function:: PyObject* PyTuple_GET_ITEM(PyObject *p, Py_ssize_t pos)

Like :c:func:`PyTuple_GetItem`, but does no checking of its arguments.

.. c:function:: PyObject* PyTuple_GetSlice(PyObject *p, Py_ssize_t low, Py_ssize_t high)

Return the slice of the tuple pointed to by *p* between *low* and *high*,

or ``NULL`` with an exception set on failure.

This is the equivalent of the Python expression ``p[low:high]``.

Indexing from the end of the tuple is not supported.

.. c:function:: int PyTuple_SetItem(PyObject *p, Py_ssize_t pos, PyObject *o)

Insert a reference to object *o* at position *pos* of the tuple pointed to by

*p*. Return ``0`` on success. If *pos* is out of bounds, return ``-1``

and set an :exc:`IndexError` exception. This function should only be used to fill in brand new tuples;

using it on an existing tuple is thread-unsafe.

.. note::

This function ":term:`steals <steal>`" a reference to *o* and discards

a reference to an item already in the tuple at the affected position

(unless it was NULL).

.. c:function:: void PyTuple_SET_ITEM(PyObject *p, Py_ssize_t pos, PyObject *o)

Like :c:func:`PyTuple_SetItem`, but does no error checking, and should *only* be

used to fill in brand new tuples, using it on an existing tuple is thread-unsafe.

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 function ":term:`steals <steal>`" a reference to *o*, and, unlike

:c:func:`PyTuple_SetItem`, does *not* discard a reference to any item that

is being replaced; any reference in the tuple at position *pos* will be

leaked.

.. warning::

This macro should *only* be used on tuples that are newly created.

Using this macro on a tuple that is already in use (or in other words, has

a refcount > 1) could lead to undefined behavior.

.. c:function:: int _PyTuple_Resize(PyObject **p, Py_ssize_t newsize)

Can be used to resize a tuple. *newsize* will be the new length of the tuple.

Because tuples are *supposed* to be immutable, this should only be used if there

is only one reference to the object. Do *not* use this if the tuple may already

be known to some other part of the code. The tuple will always grow or shrink

at the end. Think of this as destroying the old tuple and creating a new one,

only more efficiently. Returns ``0`` on success. Client code should never

assume that the resulting value of ``*p`` will be the same as before calling

this function. If the object referenced by ``*p`` is replaced, the original

``*p`` is destroyed. On failure, returns ``-1`` and sets ``*p`` to ``NULL``, and

raises :exc:`MemoryError` or :exc:`SystemError`.

.. _struct-sequence-objects:

Struct Sequence Objects

-----------------------

A struct sequence object is a :term:`named tuple`, that is, a sequence

whose items can also be accessed through attributes.

It is similar to :func:`collections.namedtuple`, but provides a slightly

different interface.

To create a struct sequence, you first have to create a specific struct sequence

type.

.. c:function:: PyTypeObject* PyStructSequence_NewType(PyStructSequence_Desc *desc)

Create a new struct sequence type from the data in *desc*, described below. Instances

of the resulting type can be created with :c:func:`PyStructSequence_New`.

Return ``NULL`` with an exception set on failure.

.. c:function:: void PyStructSequence_InitType(PyTypeObject *type, PyStructSequence_Desc *desc)

Initializes a struct sequence type *type* from *desc* in place.

.. c:function:: int PyStructSequence_InitType2(PyTypeObject *type, PyStructSequence_Desc *desc)

Like :c:func:`PyStructSequence_InitType`, but returns ``0`` on success

and ``-1`` with an exception set on failure.

.. versionadded:: 3.4

.. c:type:: PyStructSequence_Desc

Contains the meta information of a struct sequence type to create.

.. c:member:: const char *name

Fully qualified name of the type; null-terminated UTF-8 encoded.

The name must contain the module name.

.. c:member:: const char *doc

Pointer to docstring for the type or ``NULL`` to omit.

.. c:member:: PyStructSequence_Field *fields

Pointer to ``NULL``-terminated array with field names of the new type.

.. c:member:: int n_in_sequence

Number of fields visible to the Python side (if used as tuple).

.. c:type:: PyStructSequence_Field

Describes a field of a struct sequence. As a struct sequence is modeled as a

tuple, all fields are typed as :c:expr:`PyObject*`. The index in the

:c:member:`~PyStructSequence_Desc.fields` array of

the :c:type:`PyStructSequence_Desc` determines which

field of the struct sequence is described.

.. c:member:: const char *name

Name for the field or ``NULL`` to end the list of named fields,

set to :c:data:`PyStructSequence_UnnamedField` to leave unnamed.

.. c:member:: const char *doc

Field docstring or ``NULL`` to omit.

.. c:var:: const char * const PyStructSequence_UnnamedField

Special value for a field name to leave it unnamed.

.. versionchanged:: 3.9

The type was changed from ``char *``.

.. c:function:: PyObject* PyStructSequence_New(PyTypeObject *type)

Creates an instance of *type*, which must have been created with

:c:func:`PyStructSequence_NewType`.

Return ``NULL`` with an exception set on failure.

.. c:function:: PyObject* PyStructSequence_GetItem(PyObject *p, Py_ssize_t pos)

Return the object at position *pos* in the struct sequence pointed to by *p*.

The returned reference is borrowed from the struct sequence *p*

(that is: it is only valid as long as you hold a reference to *p*).

Bounds checking is performed as an assertion if Python is built in

:ref:`debug mode <debug-build>` or :option:`with assertions <--with-assertions>`.

.. c:function:: PyObject* PyStructSequence_GET_ITEM(PyObject *p, Py_ssize_t pos)

Alias to :c:func:`PyStructSequence_GetItem`.

.. versionchanged:: 3.13

Now implemented as an alias to :c:func:`PyStructSequence_GetItem`.

.. c:function:: void PyStructSequence_SetItem(PyObject *p, Py_ssize_t pos, PyObject *o)

Sets the field at index *pos* of the struct sequence *p* to value *o*. Like

:c:func:`PyTuple_SET_ITEM`, this should only be used to fill in brand new

instances.

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 function ":term:`steals <steal>`" a reference to *o*.

.. c:function:: void PyStructSequence_SET_ITEM(PyObject *p, Py_ssize_t *pos, PyObject *o)

Alias to :c:func:`PyStructSequence_SetItem`.

.. versionchanged:: 3.13

Now implemented as an alias to :c:func:`PyStructSequence_SetItem`.