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 test_head():
assert head([1]) == 1
assert head([1,2]) == 1
with pytest.raises(EmptyListError):
head([])
def test_head():
assert head([1]) == 1
assert head([1, 2]) == 1
with pytest.raises(EmptyListError):
head([])
