bpo-37178: Allow a one argument form of math.perm() (GH-13905)
diff --git a/Doc/library/math.rst b/Doc/library/math.rst
index 28ed5d21..ff937d2 100644
--- a/Doc/library/math.rst
+++ b/Doc/library/math.rst
@@ -210,7 +210,7 @@
of *x* and are floats.
-.. function:: perm(n, k)
+.. function:: perm(n, k=None)
Return the number of ways to choose *k* items from *n* items
without repetition and with order.
@@ -218,6 +218,9 @@
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 :exc:`TypeError` if either of the arguments are not integers.
Raises :exc:`ValueError` if either of the arguments are negative.