Lookahead

lookahead.py

import unittest

class Lookahead(object):
    def __init__(self, things, count):
        self.things = tuple(things)
        self.count = count
        self.windows = len(things) - count + 1

    def __iter__(self):
        return (self.things[i:i+self.count] for i in range(self.windows))
        

class LookahedTests(unittest.TestCase):
    def test_iterator(self):
        lookahead = Lookahead([1,2,"a",4,5,6,7,8,9], 4)
        iterator = iter(lookahead)
        
        self.assertEqual((1,2,"a",4), next(iterator))
        self.assertEqual((2,"a",4,5), next(iterator))
        self.assertEqual(("a",4,5,6), next(iterator))
        self.assertEqual((4,5,6,7), next(iterator))
        self.assertEqual((5,6,7,8), next(iterator))
        self.assertEqual((6,7,8,9), next(iterator))

        with self.assertRaises(StopIteration):
            next(iterator)

if __name__ == "__main__":
    unittest.main()