How Does Python Implement Sets to Achieve O(1) Membership Checking?

Set Data Structure in Python: Unveiling the Underlying Implementation

Python's set data type boasts an impressive O(1) complexity for membership checking. Understanding the internal implementation of sets sheds light on this efficient performance.

Beneath the surface, Python sets are realized using a hashtable as their underlying data structure. This arrangement allows for swift key lookups, resulting in the O(1) membership-checking runtime.

Originally, Python sets were largely derived from the implementation of dictionaries. However, over time, significant divergence has occurred between the two implementations. While both still leverage hashtables, they now exhibit different behaviors, such as arbitrary vs. insertion order, and variations in performance for specific use cases. Nonetheless, the underlying reliance on hashtables ensures an average case lookup and insertion complexity of O(1) for sets.

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