The Python Apprentice

The set constructor

Recall that somewhat confusingly, empty curly braces create an empty dictionary, rather than an empty set:

>>> d = {}>>> type(d)<class 'dict'>

To create an empty set we must resort to the set() constructor:

>>> e = set()>>> eset()

This is also the form Python echoes back to us for empty sets.

The set() constructor can create a set from any iterable series, such as a list:

>>> s = set([2, 4, 16, 64, 4096, 65536, 262144])>>> s{64, 4096, 2, 4, 65536, 16, 262144}

Duplicates in the input series are discarded. In fact, a common use of sets is to efficiently remove duplicate items from series of objects:

>>> t = [1, 4, 2, 1, 7, 9, 9]>>> set(t){1, 2, 4, 9, 7}