Frozen Sets
Immutable sets
Interview Relevant: Hashable sets
Frozen Sets
Immutable sets that can be used as dict keys.
Code Examples
Immutable frozenset for hashable needs.
python
1# Create frozenset
2fs = frozenset([1, 2, 3])
3
4# Immutable - can't add/remove
5# fs.add(4) # AttributeError!
6
7# Can use as dict key
8cache = {
9 frozenset([1, 2]): "result1",
10 frozenset([3, 4]): "result2"
11}
12
13# Set operations return frozensets
14fs1 = frozenset([1, 2, 3])
15fs2 = frozenset([2, 3, 4])
16fs1 | fs2 # frozenset({1, 2, 3, 4})
17
18# Use case: memoization key
19def cached_func(items):
20 key = frozenset(items)
21 if key in cache:
22 return cache[key]
23 # compute result...