.. highlightlang:: c

.. _setobjects:

Set Objects

-----------

.. sectionauthor:: Raymond D. Hettinger <python@rcn.com>

.. index::

   object: set

   object: frozenset

.. versionadded:: 2.5

This section details the public API for :class:`set` and :class:`frozenset`

objects.  Any functionality not listed below is best accessed using the either

the abstract object protocol (including :cfunc:`PyObject_CallMethod`,

:cfunc:`PyObject_RichCompareBool`, :cfunc:`PyObject_Hash`,

:cfunc:`PyObject_Repr`, :cfunc:`PyObject_IsTrue`, :cfunc:`PyObject_Print`, and

:cfunc:`PyObject_GetIter`) or the abstract number protocol (including

:cfunc:`PyNumber_And`, :cfunc:`PyNumber_Subtract`, :cfunc:`PyNumber_Or`,

:cfunc:`PyNumber_Xor`, :cfunc:`PyNumber_InPlaceAnd`,

:cfunc:`PyNumber_InPlaceSubtract`, :cfunc:`PyNumber_InPlaceOr`, and

:cfunc:`PyNumber_InPlaceXor`).

.. ctype:: PySetObject

   This subtype of :ctype:`PyObject` is used to hold the internal data for both

   :class:`set` and :class:`frozenset` objects.  It is like a :ctype:`PyDictObject`

   in that it is a fixed size for small sets (much like tuple storage) and will

   point to a separate, variable sized block of memory for medium and large sized

   sets (much like list storage). None of the fields of this structure should be

   considered public and are subject to change.  All access should be done through

   the documented API rather than by manipulating the values in the structure.

.. cvar:: PyTypeObject PySet_Type

   This is an instance of :ctype:`PyTypeObject` representing the Python

   :class:`set` type.

.. cvar:: PyTypeObject PyFrozenSet_Type

   This is an instance of :ctype:`PyTypeObject` representing the Python

   :class:`frozenset` type.

The following type check macros work on pointers to any Python object. Likewise,

the constructor functions work with any iterable Python object.

.. cfunction:: int PySet_Check(PyObject *p)

   Return true if *p* is a :class:`set` object or an instance of a subtype.

   .. versionadded:: 2.6

.. cfunction:: int PyFrozenSet_Check(PyObject *p)

   Return true if *p* is a :class:`frozenset` object or an instance of a

   subtype.

   .. versionadded:: 2.6

.. cfunction:: int PyAnySet_Check(PyObject *p)

   Return true if *p* is a :class:`set` object, a :class:`frozenset` object, or an

   instance of a subtype.

.. cfunction:: int PyAnySet_CheckExact(PyObject *p)

   Return true if *p* is a :class:`set` object or a :class:`frozenset` object but

   not an instance of a subtype.

.. cfunction:: int PyFrozenSet_CheckExact(PyObject *p)

   Return true if *p* is a :class:`frozenset` object but not an instance of a

   subtype.

.. cfunction:: PyObject* PySet_New(PyObject *iterable)

   Return a new :class:`set` containing objects returned by the *iterable*.  The

   *iterable* may be *NULL* to create a new empty set.  Return the new set on

   success or *NULL* on failure.  Raise :exc:`TypeError` if *iterable* is not

   actually iterable.  The constructor is also useful for copying a set

   (``c=set(s)``).

.. cfunction:: PyObject* PyFrozenSet_New(PyObject *iterable)

   Return a new :class:`frozenset` containing objects returned by the *iterable*.

   The *iterable* may be *NULL* to create a new empty frozenset.  Return the new

   set on success or *NULL* on failure.  Raise :exc:`TypeError` if *iterable* is

   not actually iterable.

   .. versionchanged:: 2.6

      Now guaranteed to return a brand-new :class:`frozenset`.  Formerly,

      frozensets of zero-length were a singleton.  This got in the way of 

      building-up new frozensets with :meth:`PySet_Add`.

The following functions and macros are available for instances of :class:`set`

or :class:`frozenset` or instances of their subtypes.

.. cfunction:: Py_ssize_t PySet_Size(PyObject *anyset)

   .. index:: builtin: len

   Return the length of a :class:`set` or :class:`frozenset` object. Equivalent to

   ``len(anyset)``.  Raises a :exc:`PyExc_SystemError` if *anyset* is not a

   :class:`set`, :class:`frozenset`, or an instance of a subtype.

.. cfunction:: Py_ssize_t PySet_GET_SIZE(PyObject *anyset)

   Macro form of :cfunc:`PySet_Size` without error checking.

.. cfunction:: int PySet_Contains(PyObject *anyset, PyObject *key)

   Return 1 if found, 0 if not found, and -1 if an error is encountered.  Unlike

   the Python :meth:`__contains__` method, this function does not automatically

   convert unhashable sets into temporary frozensets.  Raise a :exc:`TypeError` if

   the *key* is unhashable. Raise :exc:`PyExc_SystemError` if *anyset* is not a

   :class:`set`, :class:`frozenset`, or an instance of a subtype.

.. cfunction:: int PySet_Add(PyObject *set, PyObject *key)

   Add *key* to a :class:`set` instance.  Does not apply to :class:`frozenset`

   instances.  Return 0 on success or -1 on failure. Raise a :exc:`TypeError` if

   the *key* is unhashable. Raise a :exc:`MemoryError` if there is no room to grow.

   Raise a :exc:`SystemError` if *set* is an not an instance of :class:`set` or its

   subtype.

   .. versionchanged:: 2.6

      Now works with instances of :class:`frozenset` or its subtypes.

      Like :cfunc:`PyTuple_SetItem` in that it can be used to fill-in the

      values of brand new frozensets before they are exposed to other code.

The following functions are available for instances of :class:`set` or its

subtypes but not for instances of :class:`frozenset` or its subtypes.

.. cfunction:: int PySet_Discard(PyObject *set, PyObject *key)

   Return 1 if found and removed, 0 if not found (no action taken), and -1 if an

   error is encountered.  Does not raise :exc:`KeyError` for missing keys.  Raise a

   :exc:`TypeError` if the *key* is unhashable.  Unlike the Python :meth:`discard`

   method, this function does not automatically convert unhashable sets into

   temporary frozensets. Raise :exc:`PyExc_SystemError` if *set* is an not an

   instance of :class:`set` or its subtype.

.. cfunction:: PyObject* PySet_Pop(PyObject *set)

   Return a new reference to an arbitrary object in the *set*, and removes the

   object from the *set*.  Return *NULL* on failure.  Raise :exc:`KeyError` if the

   set is empty. Raise a :exc:`SystemError` if *set* is an not an instance of

   :class:`set` or its subtype.

.. cfunction:: int PySet_Clear(PyObject *set)

   Empty an existing set of all elements.