Set Objects

This section details the public API for set and frozenset objects. Any functionality not listed below is best accessed using 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).

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 all are subject to change. All access should be done through the documented API rather than by manipulating the values in the structure.

This is an instance of PyTypeObject representing the Python set 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.

Return true if p is a set object or an instance of a subtype. This function always succeeds.

Return true if p is a frozenset object or an instance of a subtype. This function always succeeds.

Return true if p is a set object, a frozenset object, or an instance of a subtype. This function always succeeds.

Return true if p is a set object but not an instance of a subtype. This function always succeeds.

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Return true if p is a set object or a frozenset object but not an instance of a subtype. This function always succeeds.

Return true if p is a frozenset object but not an instance of a subtype. This function always succeeds.

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)).

[!NOTE] The operation is atomic on free threading <free-threaded build> when iterable is a set, frozenset, dict or frozendict.

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.

[!NOTE] The operation is atomic on free threading <free-threaded build> when iterable is a set, frozenset, dict or frozendict.

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

pair: built-in function; len

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

Macro form of PySet_Size without error checking.

Return 1 if found, 0 if not found, and -1 if an error is encountered. Unlike the Python ~object.__contains__ method, this function does not automatically convert unhashable sets into temporary frozensets. Raise a TypeError if the key is unhashable. Raise SystemError if anyset is not a set, frozenset, or an instance of a subtype.

[!NOTE] The operation is atomic on free threading <free-threaded build> when key is str, int, float, bool or bytes.

Add key to a set instance. Also works with frozenset instances (like 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 TypeError if the key is unhashable. Raise a MemoryError if there is no room to grow. Raise a SystemError if set is not an instance of set or its subtype.

[!NOTE] The operation is atomic on free threading <free-threaded build> when key is str, int, float, bool or bytes.

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

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 ~set.discard method, this function does not automatically convert unhashable sets into temporary frozensets. Raise SystemError if set is not an instance of set or its subtype.

[!NOTE] The operation is atomic on free threading <free-threaded build> when key is str, int, float, bool or bytes.

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 not an instance of set or its subtype.

Empty an existing set of all elements. Return 0 on success. Return -1 and raise SystemError if set is not an instance of set or its subtype.

[!NOTE] In the free-threaded build, the set is emptied before its entries are cleared, so other threads will observe an empty set rather than intermediate states.

Deprecated API

A constant representing the size of an internal preallocated table inside PySetObject instances.

This is documented solely for completeness, as there are no guarantees that a given version of CPython uses preallocated tables with a fixed size. In code that does not deal with unstable set internals, !PySet_MINSIZE can be replaced with a small constant like 8.

If looking for the size of a set, use PySet_Size instead.

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