bpo-37178: Allow a one argument form of math.perm() (GH-13905) (GH-13919)
(cherry picked from commit e119b3d136bd94d880bce4b382096f6de3f38062)
Co-authored-by: Raymond Hettinger <rhettinger@users.noreply.github.com>
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index 9a9a815..ed11476 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -3002,7 +3002,7 @@
math.perm
n: object
- k: object
+ k: object = None
/
Number of ways to choose k items from n items without repetition and with order.
@@ -3010,18 +3010,24 @@
Evaluates to n! / (n - k)! when k <= n and evaluates
to zero when k > n.
+If k is not specified or is None, then k defaults to n
+and the function returns n!.
+
Raises TypeError if either of the arguments are not integers.
Raises ValueError if either of the arguments are negative.
[clinic start generated code]*/
static PyObject *
math_perm_impl(PyObject *module, PyObject *n, PyObject *k)
-/*[clinic end generated code: output=e021a25469653e23 input=b2e7729d9a1949cf]*/
+/*[clinic end generated code: output=e021a25469653e23 input=5311c5a00f359b53]*/
{
PyObject *result = NULL, *factor = NULL;
int overflow, cmp;
long long i, factors;
+ if (k == Py_None) {
+ return math_factorial(module, n);
+ }
n = PyNumber_Index(n);
if (n == NULL) {
return NULL;