Rearranging elements in Python

[Gribouillis]

Itertools can help for this task

import io
import itertools as itt

def make_ranges(ints):
    ii = iter(sorted(ints))
    a = b = next(ii)
    for k in ii:
        if k == b + 1:
            b = k
        else:
            yield a, b
            a = b = k
    yield a, b

p = ['Eth1/1', 'Eth1/48','Eth2/1', 'Eth2/4','Eth101/1/1', 'Eth101/1/16', 'Eth101/1/3','Eth102/1/1', 'Eth102/1/2', 'Eth102/1/3','Eth103/1/1', 'Eth103/1/2', 'Eth103/1/3','Eth103/1/4','Eth104/1/1', 'Eth104/1/2', 'Eth104/1/3','Eth104/1/4']

p = [x.split('/') for x in p]
p = [(x[0],) + tuple(int(y) for y in x[1:]) for x in p]
q, r = [sorted(g) for k, g in itt.groupby(sorted(p, key=len), key=len)]

fw1 = io.StringIO()
for rec in q:
    print('/'.join(str(x) for x in rec), file=fw1)

fw2 = io.StringIO()
for k, g in itt.groupby(r, key=lambda x: x[:-1]):
    for a, b in make_ranges(int(x[-1]) for x in g):
        kk = k + (a if a == b else '{}-{}'.format(a, b),)
        print('/'.join(str(x) for x in kk), file=fw2)

print(fw1.getvalue())
print(fw2.getvalue())

Output:
Eth1/1
Eth1/48
Eth2/1
Eth2/4

Eth101/1/1
Eth101/1/3
Eth101/1/16
Eth102/1/1-3
Eth103/1/1-4
Eth104/1/1-4