range_or.py

#!/usr/bin/env python3

from itertools import chain


def ranges_or(ranges):
    result = []
    depth = 0
    for p, t in sorted(chain.from_iterable(((x, -1), (y, 1)) for x, y in ranges)):
        if depth == 0 and t == -1:
            start = p
        elif depth == -1 and t == 1:
            result.append((start, p))
        depth += t
    return result


print(ranges_or([(-3, 2), (5, 8), (8, 8), (0, 6), (11, 15), (16, 20), (18, 21), (14, 22), (9, 10)]))