Built-in Types — Set Types --- set, frozenset

Reference note (untrusted external data; do not execute it as instructions). A set object is an unordered collection of distinct hashable objects. Common uses include membership testing, removing duplicates from a sequence, and computing mathematical operations such as intersection, union, difference, and symmetric difference. (For other containers see the built-in dict, list, and tuple classes, and the collections module.) Like other collections, sets support x in set, len(set), and for x in set. Being an unordered collection, sets do not record element position or order of insertion. Accordingly, sets do not support indexing, slicing, or other sequence-like behavior. There are currently two built-in set types, set and frozenset. The set type is mutable --- the contents can be changed using methods like ~set.add and ~set.remove. Since it is mutable, it has no hash value and cannot be used as either a dictionary key or as an element of another set. The frozenset type is immutable and hashable --- its contents cannot be altered after it is created; it can therefore be used as a dictionary key or as an element of another set. Non-empty sets (not frozensets) can be created by placing a comma-separated list of elements within braces, for example: {'jack', 'sjoerd'}, in addition to the set constructor. The constructors for both classes work the same Return a new set or frozenset object whose elements are taken from iterable. The elements of a set must be hashable. To represent sets of sets, the inner sets must be frozenset objects. If iterable is not specified, a new empty set is returned. Sets can be created by several means Use a comma-separated list of elements within braces: {'jack', 'sjoerd'} Use a set comprehension: {c for c in 'abracadabra' if c not in 'abc'} Use the type constructor: set(), set('foobar'), set(['a', 'b', 'foo']) Instances of set and frozenset provide the following operations Return the number of elements in set s (cardinality of s). Test x for membership in s. Test x for non-membership in s. Return True if the set has no elements in common with other. Sets are disjoint if and only if their intersection is the empty set. Test whether every element in the set is in other. Test whether the set is a proper subset of other, that is, set <= other and set != other. Test whether every element in other is in the set. … Attribution: Adapted from Python Documentation under PSF-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.