def test_tail():
assert tail([1]) == []
assert tail([1,2]) == [2]
assert tail([1,2,3]) == [2, 3]
with pytest.raises(EmptyListError):
tail([])
def test_tail():
assert tail([1]) == []
assert tail([1, 2]) == [2]
assert tail([1, 2, 3]) == [2, 3]
with pytest.raises(EmptyListError):
tail([])
def qsort(xs):
"""Sort a list using the quick sort algorithm."""
if not xs:
return []
else:
h = head(xs)
ts = tail(xs)
smaller = [n for n in ts if n <= h]
larger = [n for n in ts if n > h]
result = qsort(smaller) + [h] + qsort(larger)
return result
def pairs(xs):
"""Return a sequence of tuples representing all pairs of values in a list."""
if not xs:
return []
return zip(xs, tail(xs))
