Merge periods or ranges in a collection of them

unificar.py

'''
>>> periodos = [(3, 5), (7, 8), (11, 12), (-10, -1), (6, 10), (-2, 2)]
>>> periods_intersection((3, 5), (7, 8))
>>> periods_intersection((7, 8), (6, 10))
(7, 8)
>>> periods_intersection((-10, -1), (-2, 2))
(-2, -1)
>>> periods_union((-10, -1), (-2, 2))
(-10, 2)
>>> periods_union((6, 10), (7, 8))
(6, 10)
>>> list(sorted(unificar(periodos)))
[(-10, 2), (3, 5), (6, 10), (11, 12)]
'''

from functools import reduce

def periods_intersection(p1_, p2_):
    p1, p2 = sorted((p1_, p2_))
    return (p2[0], min(p1[1], p2[1])) if p1[1] >= p2[0] else None

def periods_union(p1_, p2_):
    p1, p2 = sorted((p1_, p2_))
    return (p1[0], max(p1[1], p2[1])) if p1[1] >= p2[0] else None

def unificar(periodos):
    def append_intersection(partial_periods, next_period):
        if partial_periods and periods_intersection(partial_periods[-1], next_period):
            partial_periods[-1] = periods_union(partial_periods[-1], next_period)
        else:
            partial_periods.append(next_period)
        return partial_periods
    return reduce(append_intersection, sorted(periodos), [])