experiments/combinaisons.py

   1 from __future__ import generators
   2 #!/usr/bin/env python
   3
   4 __version__ = "1.0"
   5
   6 """xpermutations.py
   7 Generators for calculating a) the permutations of a sequence and
   8 b) the combinations and selections of a number of elements from a
   9 sequence. Uses Python 2.2 generators.
  10
  11 Similar solutions found also in comp.lang.python
  12
  13 Keywords: generator, combination, permutation, selection
  14
  15 See also: http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/105962
  16 See also: http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/66463
  17 See also: http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/66465
  18 """
  19
  20
  21 def xcombinations(items, n):
  22     if n==0: yield []
  23     else:
  24         for i in xrange(len(items)):
  25             for cc in xcombinations(items[:i]+items[i+1:],n-1):
  26                 yield [items[i]]+cc
  27
  28 def xuniqueCombinations(items, n):
  29     if n==0: yield []
  30     else:
  31         for i in xrange(len(items)):
  32             for cc in xuniqueCombinations(items[i+1:],n-1):
  33                 yield [items[i]]+cc
  34
  35 def xselections(items, n):
  36     if n==0: yield []
  37     else:
  38         for i in xrange(len(items)):
  39             for ss in xselections(items, n-1):
  40                 yield [items[i]]+ss
  41
  42 def xpermutations(items):
  43     return xcombinations(items, len(items))
  44
  45 if __name__=="__main__":
  46     print "Permutations of 'love'"
  47     for p in xpermutations(['l','o','v','e']): print ''.join(p)
  48
  49     print
  50     print "Combinations of 2 letters from 'love'"
  51     for c in xcombinations(['l','o','v','e'],2): print ''.join(c)
  52
  53     print
  54     print "Unique Combinations of 2 letters from 'love'"
  55     for uc in xuniqueCombinations(['l','o','v','e'],2): print ''.join(uc)
  56
  57     print
  58     print "Selections of 2 letters from 'love'"
  59     for s in xselections(['l','o','v','e'],2): print ''.join(s)
  60
  61     print
  62     print map(''.join, list(xpermutations('done')))