Is set ordered or unordered in Python?

Is set ordered or unordered in Python?

Last Updated : 08 Dec, 2024

A set is generally considered unordered. This means that the elements of a set do not have a guaranteed order. Unlike lists or arrays, where the order of items is preserved the elements in a set are stored without any specific sequence.

For instance, if you create a set and add items to it, there's no guarantee that the items will appear in the same order every time you access them. For example:

Python

s = {3, 1, 2}
print(s)

Output

{1, 2, 3}

The output might be {1, 2, 3}, {3, 2, 1}, or another random order. This lack of order is characteristic of sets in languages like Python.

Why Are Sets Unordered?

The lack of order in sets is intentional. Sets are designed to focus on unique elements and the efficiency of operations like checking membership (i.e., in) or adding/removing elements is prioritized. By not worrying about the order, sets can offer faster performance for these operations.

The underlying data structure for a set is typically a hash table which doesn't maintain the order of elements. Instead, it uses a hash function to store and retrieve items, allowing quick lookups but no guarantee of order.

Is set ordered or unordered in Python?

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