.. highlightlang:: c

Set Objects

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

.. index::
 object: set
 object: frozenset

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 :c:func:`PyObject_CallMethod`, :c:func:`PyObject_RichCompareBool`, :c:func:`PyObject_Hash`, :c:func:`PyObject_Repr`, :c:func:`PyObject_IsTrue`, :c:func:`PyObject_Print`, and :c:func:`PyObject_GetIter`) or the abstract number protocol (including :c:func:`PyNumber_And`, :c:func:`PyNumber_Subtract`, :c:func:`PyNumber_Or`, :c:func:`PyNumber_Xor`, :c:func:`PyNumber_InPlaceAnd`, :c:func:`PyNumber_InPlaceSubtract`, :c:func:`PyNumber_InPlaceOr`, and :c:func:`PyNumber_InPlaceXor`).

.. c:type:: PySetObject

 This subtype of :c:type:`PyObject` is used to hold the internal data for both
 :class:`set` and :class:`frozenset` objects. It is like a :c:type:`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.

.. c:var:: PyTypeObject PySet_Type

 This is an instance of :c:type:`PyTypeObject` representing the Python
 :class:`set` type.

.. c:var:: PyTypeObject PyFrozenSet_Type

 This is an instance of :c:type:`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.

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

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

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

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

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

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

.. c:function:: 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.

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

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

.. c:function:: 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)``).

.. c:function:: 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.

The following functions and macros are available for instances of :class:`set` or :class:`frozenset` or instances of their subtypes.

.. c:function:: 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.

.. c:function:: Py_ssize_t PySet_GET_SIZE(PyObject *anyset)

 Macro form of :c:func:`PySet_Size` without error checking.

.. c:function:: 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.

.. c:function:: int PySet_Add(PyObject *set, PyObject *key)

 Add *key* to a :class:`set` instance. Also works with :class:`frozenset`
 instances (like :c:func:`PyTuple_SetItem` it can be used to fill-in the values
 of brand new frozensets before they are exposed to other code). 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 not an instance of :class:`set` or its
 subtype.

The following functions are available for instances of :class:`set` or its subtypes but not for instances of :class:`frozenset` or its subtypes.

.. c:function:: 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:`~set.discard`
 method, this function does not automatically convert unhashable sets into
 temporary frozensets. Raise :exc:`PyExc_SystemError` if *set* is not an
 instance of :class:`set` or its subtype.

.. c:function:: 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 not an instance of
 :class:`set` or its subtype.

.. c:function:: int PySet_Clear(PyObject *set)

 Empty an existing set of all elements.

.. c:function:: int PySet_ClearFreeList()

 Clear the free list. Return the total number of freed items.

 .. versionadded:: 3.3

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