combinations.py

   1 from __future__ import generators
   2
   3 def xcombinations(items, n):
   4     if n==0: yield []
   5     else:
   6         for i in xrange(len(items)):
   7             for cc in xcombinations(items[:i]+items[i+1:],n-1):
   8                 yield [items[i]]+cc
   9
  10 def xuniqueCombinations(items, n):
  11     if n==0: yield []
  12     else:
  13         for i in xrange(len(items)):
  14             for cc in xuniqueCombinations(items[i+1:],n-1):
  15                 yield [items[i]]+cc
  16
  17 def xselections(items, n):
  18     if n==0: yield []
  19     else:
  20         for i in xrange(len(items)):
  21             for ss in xselections(items, n-1):
  22                 yield [items[i]]+ss
  23
  24 def xpermutations(items):
  25     return xcombinations(items, len(items))
  26