fiddle.py

from time import time

starts = [
    1248637121,
    1248818005,
    1248819043,
    1248819661,
    1248820029,
    1248862668,
    1248976328,
    1248989370,
    1249036736,
]

stops = [
    1248817256,
    1248817974,
    1248819674,
    1248819680,
    1248819813,
    1248819936,
    1248819977,
    1248820035,
    1248820188,
    1248873042,
    1248978031,
    1248992420,
    1249036746,
]

def zip_to_type(starts, stops):
    tuples = []
    for start in starts:
        tuples.append(('start', start))
    for stop in stops:
        tuples.append(('stop', stop))

    def key_gen(tuple):
        return tuple[1]

    tuples = sorted(tuples, key=key_gen)

    return tuples


def flush_until_different(type, tuples):
    removals = []
    for tuple in tuples:
        if tuple[0] == type:
            removals.append(tuple)
        else:
            break
    return removals


def de_gap(type, tuples):
    if type == 'stop':
        tuples.reverse()

    index = 0
    removals = []

    for tuple in tuples:
        if tuple[0] == type:
            removals.extend(flush_until_different(type, tuples[index + 1:]))
        index += 1

    for removeme in removals:
        try:
            tuples.remove(removeme)
        except ValueError:
            pass

    if type == 'stop':
        tuples.reverse()
    return tuples


def totaller(tuples):
    total = 0
    while 1:
        try:
            try:
                start = tuples.pop(0)[1]
            except IndexError:
                raise
            try:
                stop = tuples.pop(0)[1]
            except IndexError:
                stop = time()
        except IndexError:
            return total
        total += (stop - start)


def count_times(starts, stops):
    return totaller(
        de_gap('stop',
            de_gap('start',
                zip_to_type(starts, stops))))


if __name__ == '__main__':
    print "with stopper"
    seconds = count_times(starts, stops)
    print float(seconds)/(60*60), 'hours'

    print "without stopper"
    stops.pop()
    seconds = count_times(starts, stops)
    print float(seconds)/(60*60), 'hours'