CODEWITHSUNDEEP
pythondata-structuressettuples
legends2k
legends2k

Reputation: 32964

Difference between tuples and frozensets in Python

I'm learning Python 3 using The Quick Python Book, where the author talks about frozensets, stating that since sets are mutable and hence unhashable, thereby becoming unfit for being dictionary keys, their frozen counterparts were introduced. Other than the obvious difference that a tuple is an ordered data structure while frozenset, or more generally a set, is unordered, are there any other differences between a tuple and a frozenset?

Upvotes: 69

Views: 36886

Answers (5)

Ravi Kishan
Ravi Kishan

Reputation: 21

A tuple can store duplicate values, while a frozenset enforces uniqueness. Tuples allow element access by index, but frozensets do not support indexing or slicing. Frozensets support set operations like union, intersection, and difference, whereas tuples lack these. Additionally, a tuple's hashability depends on its elements (it must contain only hashable items), while a frozenset is always hashable since it contains only immutable elements. Lastly, tuples preserve insertion order (since Python 3.7+), while frozensets are unordered, meaning iteration order is not guaranteed.

Check out this reference

Upvotes: 1

F1Rumors
F1Rumors

Reputation: 948

Somewhat counter intuitive - what about this bon mot:

sss = frozenset('abc')
sss |= set('efg')

Will yield:

frozenset(['a', 'c', 'b', 'e', 'g', 'f'])

Of course, this is equivalent to x = x | y, so not changing the original frozenset, but it doesn't half make a mockery of the term 'immutable' to the code reviewer!

Upvotes: 14

Joop
Joop

Reputation: 8108

Volatility does mention that frozensets are not indexed. I was looking at the other functionality, so did not immediately realize that standard python slicing is not possible.

a = frozenset((1, 1, 1, 1, 2, 2, 2))  # results in frozenset([1, 2])
print a[0]

will give error:

TypeError: 'frozenset' object does not support indexing

Obvious from fact that it is not indexed, but though it was worth adding explicitly here

Upvotes: 5

Volatility
Volatility

Reputation: 32310

tuples are immutable lists, frozensets are immutable sets.

tuples are indeed an ordered collection of objects, but they can contain duplicates and unhashable objects, and have slice functionality

frozensets aren't indexed, but you have the functionality of sets - O(1) element lookups, and functionality such as unions and intersections. They also can't contain duplicates, like their mutable counterparts.

Upvotes: 114

Makoto
Makoto

Reputation: 106470

One difference that comes to mind is the issue of duplicates. A tuple of (1, 1, 1, 1, 2, 2, 2) would be exactly what you expect, but a frozenset would remove all of those duplicates, leaving you with frozenset([1, 2]).

Upvotes: 7

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