
Set Objects
***********

New in version 2.5.

This section details the public API for ``set`` and ``frozenset``
objects.  Any functionality not listed below is best accessed using
the either the abstract object protocol (including
``PyObject_CallMethod``, ``PyObject_RichCompareBool``,
``PyObject_Hash``, ``PyObject_Repr``, ``PyObject_IsTrue``,
``PyObject_Print``, and ``PyObject_GetIter``) or the abstract number
protocol (including ``PyNumber_And``, ``PyNumber_Subtract``,
``PyNumber_Or``, ``PyNumber_Xor``, ``PyNumber_InPlaceAnd``,
``PyNumber_InPlaceSubtract``, ``PyNumber_InPlaceOr``, and
``PyNumber_InPlaceXor``).

PySetObject

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

PyTypeObject PySet_Type

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

PyTypeObject PyFrozenSet_Type

   This is an instance of ``PyTypeObject`` representing the Python
   ``frozenset`` type.

The following type check macros work on pointers to any Python object.
Likewise, the constructor functions work with any iterable Python
object.

int PySet_Check(PyObject *p)

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

   New in version 2.6.

int PyFrozenSet_Check(PyObject *p)

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

   New in version 2.6.

int PyAnySet_Check(PyObject *p)

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

int PyAnySet_CheckExact(PyObject *p)

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

int PyFrozenSet_CheckExact(PyObject *p)

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

PyObject* PySet_New(PyObject *iterable)
    Return value: New reference.

   Return a new ``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 ``TypeError`` if
   *iterable* is not actually iterable.  The constructor is also
   useful for copying a set (``c=set(s)``).

PyObject* PyFrozenSet_New(PyObject *iterable)
    Return value: New reference.

   Return a new ``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 ``TypeError`` if *iterable* is not actually iterable.

   Changed in version 2.6: Now guaranteed to return a brand-new
   ``frozenset``.  Formerly, frozensets of zero-length were a
   singleton.  This got in the way of building-up new frozensets with
   ``PySet_Add()``.

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

Py_ssize_t PySet_Size(PyObject *anyset)

   Return the length of a ``set`` or ``frozenset`` object. Equivalent
   to ``len(anyset)``.  Raises a ``PyExc_SystemError`` if *anyset* is
   not a ``set``, ``frozenset``, or an instance of a subtype.

Py_ssize_t PySet_GET_SIZE(PyObject *anyset)

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

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 ``__contains__()`` method, this
   function does not automatically convert unhashable sets into
   temporary frozensets.  Raise a ``TypeError`` if the *key* is
   unhashable. Raise ``PyExc_SystemError`` if *anyset* is not a
   ``set``, ``frozenset``, or an instance of a subtype.

int PySet_Add(PyObject *set, PyObject *key)

   Add *key* to a ``set`` instance.  Does not apply to ``frozenset``
   instances.  Return 0 on success or -1 on failure. Raise a
   ``TypeError`` if the *key* is unhashable. Raise a ``MemoryError``
   if there is no room to grow. Raise a ``SystemError`` if *set* is an
   not an instance of ``set`` or its subtype.

   Changed in version 2.6: Now works with instances of ``frozenset``
   or its subtypes. Like ``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 ``set`` or its
subtypes but not for instances of ``frozenset`` or its subtypes.

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 ``KeyError`` for
   missing keys.  Raise a ``TypeError`` if the *key* is unhashable.
   Unlike the Python ``discard()`` method, this function does not
   automatically convert unhashable sets into temporary frozensets.
   Raise ``PyExc_SystemError`` if *set* is an not an instance of
   ``set`` or its subtype.

PyObject* PySet_Pop(PyObject *set)
    Return value: New reference.

   Return a new reference to an arbitrary object in the *set*, and
   removes the object from the *set*.  Return *NULL* on failure.
   Raise ``KeyError`` if the set is empty. Raise a ``SystemError`` if
   *set* is an not an instance of ``set`` or its subtype.

int PySet_Clear(PyObject *set)

   Empty an existing set of all elements.
