A Python set type designed for dense sets of non-negative integers. Each element is represented as a 1 bit in the corresponding position within a Python int.

Membership test n in s is O(1) because the bit that represents n in the s set is in word n // 64, at bit offset n % 64 in the internal representation of the int.

Adding an element means setting a bit at the corresponding offset.

Set operations such as union, intersection, and symmetric difference are implemented using the bitwise operators |, &, and ^ on the int values that store the bits.

This package is inspired by the intset example in chapter 6 of The Go Programming Language, by Donovan & Kernighan.