How do Python sets achieve O(1) membership checking?

Understanding the Implementation of Sets in Python

In Python, sets offer efficient membership checking with an O(1) time complexity. Delving into the implementation reveals a hashtable as the underlying data structure that supports this performance.

The set implementation borrows elements from the dictionary implementation, essentially utilizing dictionaries with dummy values to represent set members. However, it employs optimizations to exploit the absence of values, resulting in the exceptional membership-checking behavior.

Examining the CPython source code for sets provides further insight. While initially derived from the dictionary implementation, the implementations have since diverged significantly. Despite these deviations, sets continue to utilize hashtables to maintain O(1) lookup and insertion operations.

Understanding the data structure underlying sets highlights their performance advantages and paves the way for informed optimization decisions within Python programs.

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