Expert Python Programming - Third Edition

Sets

Sets are a very robust data structure that are mostly useful in situations where the order of elements is not as important as their uniqueness. They are also useful if you need to efficiently check efficiency if the element is contained in a collection. Sets in Python are generalizations of mathematic sets, and are provided as built-in types in two flavors:

• set(): This is a mutable, non-ordered, finite collection of unique, immutable (hashable) objects
• frozenset(): This is an immutable, hashable, non-ordered collection of unique, immutable (hashable) objects

The immutability of frozenset() objects makes it possible for them to be included as dictionary keys and also other set() and frozenset() elements. A plain mutable set() object ...