combi.py

"""Just simple combination

todo recursive call s should be call by reference
"""
import itertools
import string
import unittest


def combination(s, n):
    if n < 1:
        yield ()
    elif n == 1:
        for i in s:
            yield i,
    else:
        for i in xrange(len(s)):
            for j in combination(s[i+1:], n-1):
                yield (s[i],) + j

class CombiTest(unittest.TestCase):
    def setUp(self):
        self.data = string.lowercase

    def test_compare_with_itertools(self):
        for x in range(5):
            sol = tuple(combination(self.data, x))
            exp = tuple(itertools.combinations(self.data, x))
            self.assertEqual(exp, sol)