python merge set of fronzensets into one set

Question

I am trying to merge sets defined in a set and this is what I have now

a = frozenset([1,3,4])
b = frozenset([1,2,3,4,5])
s = set()
s.add(a)
s.add(b)
merged = set(itertools.chain.from_iterable(s))

In practice, s may contain many frozensets. Is there better ways to do it? It feels like a reduce case, but

from functools import reduce
merged = reduce(|, s)

doesn't work.

Also

merged = reduce(set.add, s)

doesn't work because the elements of s are frozensets.

Answer 1

If you have more than two frozensets, create a container (e.g., list) of them and apply a union:

listoffrozensets = [a,b,...]
frozenset().union(*listoffrozensets)

Answer 2

You can use reduce, just use the appropriate function:

>>> from functools import reduce
>>> frozenset.union
<method 'union' of 'frozenset' objects>
>>> reduce(frozenset.union, [a,b])
frozenset({1, 2, 3, 4, 5})
>>>

You were on the right track with |, but | is an operator in Python, and can't be substituted for a function. But when you want to do that, import the operator!

>>> import operator
>>> reduce(operator.or_, [a,b])
frozenset({1, 2, 3, 4, 5})