Unfolding the lists

Unfold the list with ranges, sort and regroup

o = ['12-15', '40003', '40012', '71842-71844', '71848-71851',
     '71853-54', '72717-72721', '72724-72732', '72734', '72787',
     '68344', '46', '48', '49', '68351-68354', '68358', '59',
    ]

def r(s):
    if '-' in s:
        a, b = map(int, s.split('-'))
        if b < a:
            sa, sb = map(str, (a, b))
            la, lb = map(len, (sa, sb))
            sb = sa[:la-lb] + sb
            b = int(sb)
        return list(range(a, b+1))
    else:
        return [int(s),]


def r2(q):
    b = q.pop()
    while True:
        try:
            a = b
            prev = None

            b = q.pop()

            prev = a
            while (b == prev + 1):
                prev = b
                b = q.pop()

            if prev and a!=prev:
                yield '-'.join(map(str, (a, prev)))
            else:
                yield str(a)
        except IndexError:
            if prev and a!=prev:
                yield '-'.join(map(str, (a, prev)))
                return
            else:
                yield str(a)
                return



z = []
for x in o:
    z.extend(r(x))

for i in range(len(z) - 1):
    a, b = z[i], z[i+1]
    if a>1000 and b < 1000:
        sa, sb = map(str, (a, b))
        la, lb = map(len, (sa, sb))
        sb = sa[:la-lb] + sb
        b = int(sb)
    z[i+1] = b

# We have a full unwrapped list here (z)
z1 = sorted(set(z))
# Saved to z1

z = sorted(set(z), reverse=True)

z2 = list(r2(z))
# So we have new folded list here (z2)

Src | Discussion

https://gist.github.com/vpag/1358a52d64d515079426