7.5.13 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_Add(), PyNumber_Subtract(), PyNumber_Or(), PyNumber_Xor(), PyNumber_InplaceAdd(), PyNumber_InplaceSubtract(), PyNumber_InplaceOr(), and PyNumber_InplaceXor()). Note, PyNumber_InplaceSubtract() is also useful clearing clearing a set (s-=s).

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 PyAnySet_Check( PyObject *p): Returns true if p is a set object, a frozenset object, or an instance of a subtype.

int PyAnySet_CheckExact( PyObject *p): Returns true if p is a set object or a frozenset object but not an instance of a subtype.

int PyFrozenSet_CheckExact( PyObject *p): Returns true if p is a frozenset object but not an instance of a subtype.

PyObject* PySet_New( PyObject *iterable): Returns a new set containing objects returned by the iterable. The iterable may be NULL to create a new empty set. Returns the new set on success or NULL on failure. Raises TypeError if iterable is not actually iterable. The constructor is also useful for copying a set (c=set(s)).

PyObject* PyFrozenSet_New( PyObject *iterable): Returns a new frozenset containing objects returned by the iterable. The iterable may be NULL to create a new empty frozenset. Returns the new set on success or NULL on failure. Raises TypeError if iterable is not actually iterable.

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

int PySet_Size( PyObject *anyset): Returns 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.

int PySet_GET_SIZE( PyObject *anyset): Macro form of PySet_Size() without error checking.

int PySet_Contains( PyObject *anyset, PyObject *key): Returns 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. Raises a TypeError if the key is unhashable. Raises PyExc_SystemError if anyset is not a set, frozenset, or an instance of a subtype.

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

int PySet_Add( PyObject *set, PyObject *key): Adds key to a set instance. Does not apply to frozenset instances. Returns 0 on success or -1 on failure. Raises a TypeError if the key is unhashable. Raises a MemoryError if there is no room to grow. Raises a SystemError if set is an not an instance of set or its subtype.

int PySet_Discard( PyObject *set, PyObject *key): Returns 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. Raises a TypeError if the key is unhashable. Unlike the Python discard() method, this function does not automatically convert unhashable sets into temporary frozensets. Raises PyExc_SystemError if set is an not an instance of set or its subtype.

PyObject* PySet_Pop( PyObject *set): Return value: Borrowed reference.
Returns a new reference to an arbitrary object in the set, and removes the object from the set. Returns NULL on failure. Raises KeyError if the set is empty. Raises a SystemError if set is an not an instance of set or its subtype.

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