enumerate all subsequences in a sequence

gistfile1.py

# enumerate all subsequences in a sequence

def subsequences(s):
    for i in range(len(s)):
        for j in range(len(s) - i):
            yield s[j:j + i + 1]

if __name__ == '__main__':
    assert list(subsequences([])) == []
    assert list(subsequences([1])) == [[1]]
    assert list(subsequences([1, 2])) == [[1], [2], [1,2]]
    assert list(subsequences([1, 2, 3])) == [[1], [2], [3], [1,2], [2,3], [1,2,3]]
    assert list(subsequences((1, 2, 3))) == [(1,), (2,), (3,), (1,2), (2,3), (1,2,3)]
    assert list(subsequences('abc')) == ['a', 'b', 'c', 'ab', 'bc', 'abc']