Welcome, guest | Sign In | My Account | Store | Cart
```#!/usr/bin/env python

__version__ = "1.0"

"""xpermutations.py
Generators for calculating a) the permutations of a sequence and
b) the combinations and selections of a number of elements from a
sequence. Uses Python 2.2 generators.

Similar solutions found also in comp.lang.python

Keywords: generator, combination, permutation, selection

"""

from __future__ import generators

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))

if __name__=="__main__":
print "Permutations of 'love'"
for p in xpermutations(['l','o','v','e']): print ''.join(p)

print
print "Combinations of 2 letters from 'love'"
for c in xcombinations(['l','o','v','e'],2): print ''.join(c)

print
print "Unique Combinations of 2 letters from 'love'"
for uc in xuniqueCombinations(['l','o','v','e'],2): print ''.join(uc)

print
print "Selections of 2 letters from 'love'"
for s in xselections(['l','o','v','e'],2): print ''.join(s)

print
print map(''.join, list(xpermutations('done')))
```