Python 3 - Second Edition

13.2    Sets: set and frozenset

A set is a unordered collection of elements in which each element may be contained only once. In Python, there are two basic data types for representing sets: set for a mutable set and frozenset for an immutable set.

13.2.1    Creating a Set

Note that whether a mutable or an immutable set is instantiated, a set can contain only immutable elements. Table 13.1 provides an overview of the basic data types and their mutability. For example, if you try to create a set that should contain a list as an element, the interpreter reports a corresponding error:

>>> set([1, 2, list()])Traceback (most recent call last):  File "<python-input-3>", line 1, in <module>    set([1, 2, list()])    ~~~^^^^^^^^^^^^^^^^TypeError: cannot use ...