def test_n_permutations_edges():
with pytest.raises(ValueError):
n_permutations(-1, 1)
with pytest.raises(ValueError):
n_permutations(1, -1)
assert n_permutations(0, 0) == 0
assert n_permutations(2, 3) == 0
assert n_permutations(5) == n_permutations(5, 5)
def permutations(self, r: Optional[int] = None):
"""See itertools.permutations_
.. _itertools.permutations: https://docs.python.org/3/library/itertools.html#itertools.permutations
""" # noqa
this_len = len_or_none(self)
if this_len is None:
length = None
else:
length = n_permutations(this_len, r)
return FIt(permutations(self, r), length)
def test_n_permutations():
assert n_permutations(3, 2) == 6