Need to store task metadata that should not change? Use a tuple for fixed values such as creation time and user, and a list for tasks you expect to add or remove. A tuple makes the intention visible and prevents reassignment of its items. It also uses less memory than a list holding the same data. section 3.1.1
A tuple rejects updates
metadata = ("Monday", "Alex") metadata[0] = "Tuesday" # TypeError: 'tuple' object does not support item assignment A tuple also has no append method; calling one raises AttributeError. Choose a list instead when updates are part of the job. section 3.1.1
The protection applies to the tuple’s items, not necessarily to objects inside it. If an item is a list, you can still change that list: section 3.1.3
An inner list can still change
numbers = ([1, 2], [1, 2]) numbers[0].append(3) # numbers is now ([1, 2, 3], [1, 2]) The tuple still refers to the same inner list. Use the distinction when deciding whether a container really protects the data you care about. section 3.1.3
Immutability also matters for hashing: changing an object’s contents conflicts with the expectation of a consistent hash value. Lists, dictionaries, and sets are unhashable; hashability can be checked with collections.abc.Hashable. For record-like data, named tuples are immutable, while ordinary data classes are mutable. Set @dataclass(frozen=True) when a data class’s fields should resist reassignment. section 3.5.2 section 9.2.3
