class _Base:

    def __init__(self, iterable):
        self._list = list(iterable)

    def __len__(self):
        return len(self._list)

    def __getitem__(self, index):
        return self._list[index]

class Classic(_Base): pass
class New(_Base, object): pass

for l in range(2, 5):
    for cls in (New, Classic):
        a = cls(range(l))
        print 'a = %s(%s)' % (cls.__name__, a[:])
        for val in range(1, l):
            stmt = 'a[-%s:]' % (l + val)
            print '\t', stmt, '=', eval(stmt)
    print


## Output
#
#a = New([0, 1])
#	a[-3:] = [0, 1]
#a = Classic([0, 1])
#	a[-3:] = [1]
#
#a = New([0, 1, 2])
#	a[-4:] = [0, 1, 2]
#	a[-5:] = [0, 1, 2]
#a = Classic([0, 1, 2])
#	a[-4:] = [2]
#	a[-5:] = [1, 2]
#
#a = New([0, 1, 2, 3])
#	a[-5:] = [0, 1, 2, 3]
#	a[-6:] = [0, 1, 2, 3]
#	a[-7:] = [0, 1, 2, 3]
#a = Classic([0, 1, 2, 3])
#	a[-5:] = [3]
#	a[-6:] = [2, 3]
#	a[-7:] = [1, 2, 3]