combinations.py

import itertools
import re
l = ['A', 'S', 'U', 'T']
mask = ''.join(reversed(l))
for i in range(1,len(l)+1):
    for comb in itertools.combinations(l, i):
        reg = "[^%s]" % ''.join(comb)
        print re.sub(reg,"-", mask)