Python frozenset() built-in function
From the Python 3 documentation
Return a new frozenset object, optionally with elements taken from iterable. frozenset is a built-in class. See frozenset and Set Types — set, frozenset for documentation about this class.
Examples
>>> frozenset([1, 2, 3])
# frozenset({1, 2, 3})
>>> frozenset({1, 2, 3})
# frozenset({1, 2, 3})
>>> frozenset((1, 2, 3))
# frozenset({1, 2, 3})