Python High Performance - Second Edition

Sets

Sets are unordered collections of elements, with the additional restriction that the elements must be unique.  The main use-cases where sets are a good choice are membership tests (testing if an element is present in the collection) and, unsurprisingly, set operations such as union, difference, and intersection.

In Python, sets are implemented using a hash-based algorithm just like dictionaries; therefore, the time complexities for addition, deletion, and test for membership scale as O(1) with the size of the collection.

Sets contain only unique elements. An immediate use case of sets is the removal of duplicates from a collection, which can be accomplished by simply passing the collection through the set constructor, as follows:

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