permutations.py

def getPermutations(a):
   if len(a)==1:
      yield a
   else:
      for i in range(len(a)):
         this = a[i]
         rest = a[:i] + a[i+1:]
         for p in getPermutations(rest):
            yield this + p

def xcombinations(items, n):
    if n==0: yield []
    else:
        for i in xrange(len(items)):
            for cc in xcombinations(items[:i]+items[i+1:],n-1):
                yield [items[i]]+cc

def xuniqueCombinations(items, n):
    if n==0: yield []
    else:
        for i in xrange(len(items)):
            for cc in xuniqueCombinations(items[i+1:],n-1):
                yield [items[i]]+cc
            
def xselections(items, n):
    if n==0: yield []
    else:
        for i in xrange(len(items)):
            for ss in xselections(items, n-1):
                yield [items[i]]+ss

def xpermutations(items):
    return xcombinations(items, len(items))