python convert list of numbers into ranges.

convert2range.py

import re
from itertools import groupby
from collections import OrderedDict

# define list of interfaces
a = ['swp2100', 'bond12.100', 'swp22', 'br20',
     'bond0', 'bond22', 'port-channel5']
b = OrderedDict()

# group ports based on int name before digit
f = lambda x: re.match(r'([a-z_-]+)\d+', x.lower()).group(1)
gb = groupby(a, f)
for k, a in gb: 
    try:
        b[k] = b[k] + map(str, a)
    except:
        b[k] = map(str, a)

"create a new dict with sorted keys"
newdct = OrderedDict((key, b[key]) for key in sorted(b.keys()))
print newdct