python - How to create the union of many sets using a generator expression?

Question

Suppose I have a list of sets and I want to get the union over all sets in that list. Is there any way to do this using a generator expression? In other words, how can I create the union over all sets in that list directly as a frozenset?

Answer 1

Just use the .union() method.

>>> l = [set([1,2,3]), set([4,5,6]), set([1,4,9])]
>>> frozenset().union(*l)
frozenset([1, 2, 3, 4, 5, 6, 9])

This works for any iterable of iterables.