def unique(items, key=None):
'''It yields the unique items.
The items must be sorted. It only compares contiguous items.
'''
return (first(groups[1]) for groups in groupby(items, key))
def test_interpose():
assert "a" == first(rest(interpose("a", range(1000000000))))
assert "tXaXrXzXaXn" == "".join(interpose("X", "tarzan"))
assert list(interpose(0, itertools.repeat(1, 4))) == [1, 0, 1, 0, 1, 0, 1]
assert list(interpose(".", ["a", "b", "c"])) == ["a", ".", "b", ".", "c"]
def test_first():
assert first("ABCDE") == "A"
assert first((3, 2, 1)) == 3
assert isinstance(first({0: "zero", 1: "one"}), int)
def test_first():
assert first('ABCDE') == 'A'
assert first((3, 2, 1)) == 3
def test_interpose():
assert "a" == first(rest(interpose("a", range(10000000000))))
assert "tXaXrXzXaXn" == "".join(interpose("X", "tarzan"))
def test_first():
assert first('ABCDE') == 'A'
assert first((3, 2, 1)) == 3
assert isinstance(first({0: 'zero', 1: 'one'}), int)
def test_first():
assert first('ABCDE') == 'A'
assert first((3, 2, 1)) == 3
def test_interpose():
assert "a" == first(rest(interpose("a", range(10000000000))))
assert "tXaXrXzXaXn" == "".join(interpose("X", "tarzan"))