[Python-checkins] bpo-37178: Allow a one argument form of math.perm() (GH-13905) (GH-13919)

Sat Jun 8 12:17:38 EDT 2019

https://github.com/python/cpython/commit/feaceaafe816e95c4aff15eab0bea6dc2bbfe4fd
commit: feaceaafe816e95c4aff15eab0bea6dc2bbfe4fd
branch: 3.8
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: Raymond Hettinger <rhettinger at users.noreply.github.com>
date: 2019年06月08日T09:17:33-07:00
summary:
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 at users.noreply.github.com>
files:
A Misc/NEWS.d/next/Library/2019-06-07-17-11-34.bpo-37178.b1StSv.rst
A Misc/NEWS.d/next/Library/2019-06-07-17-16-09.bpo-37178.Day_oB.rst
M Doc/library/math.rst
M Lib/test/test_math.py
M Modules/clinic/mathmodule.c.h
M Modules/mathmodule.c

diff --git a/Doc/library/math.rst b/Doc/library/math.rst
index 28ed5d21f03a..ff937d27c6ce 100644
--- a/Doc/library/math.rst
+++ b/Doc/library/math.rst
@@ -210,7 +210,7 @@ Number-theoretic and representation functions
 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 @@ Number-theoretic and representation functions
 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.
 
diff --git a/Lib/test/test_math.py b/Lib/test/test_math.py
index 86e3923af6d0..adefa07a4041 100644
--- a/Lib/test/test_math.py
+++ b/Lib/test/test_math.py
@@ -1885,8 +1885,13 @@ def testPerm(self):
 self.assertEqual(perm(n, 1), n)
 self.assertEqual(perm(n, n), factorial(n))
 
+ # Test one argument form
+ for n in range(20):
+ self.assertEqual(perm(n), factorial(n))
+ self.assertEqual(perm(n, None), factorial(n))
+
 # Raises TypeError if any argument is non-integer or argument count is
- # not 2
+ # not 1 or 2
 self.assertRaises(TypeError, perm, 10, 1.0)
 self.assertRaises(TypeError, perm, 10, decimal.Decimal(1.0))
 self.assertRaises(TypeError, perm, 10, "1")
@@ -1894,7 +1899,7 @@ def testPerm(self):
 self.assertRaises(TypeError, perm, decimal.Decimal(10.0), 1)
 self.assertRaises(TypeError, perm, "10", 1)
 
- self.assertRaises(TypeError, perm, 10)
+ self.assertRaises(TypeError, perm)
 self.assertRaises(TypeError, perm, 10, 1, 3)
 self.assertRaises(TypeError, perm)
 
diff --git a/Misc/NEWS.d/next/Library/2019-06-07-17-11-34.bpo-37178.b1StSv.rst b/Misc/NEWS.d/next/Library/2019-06-07-17-11-34.bpo-37178.b1StSv.rst
new file mode 100644
index 000000000000..77b872319a91
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-06-07-17-11-34.bpo-37178.b1StSv.rst
@@ -0,0 +1,2 @@
+For math.perm(n, k), let k default to n, giving the same result as
+factorial.
diff --git a/Misc/NEWS.d/next/Library/2019-06-07-17-16-09.bpo-37178.Day_oB.rst b/Misc/NEWS.d/next/Library/2019-06-07-17-16-09.bpo-37178.Day_oB.rst
new file mode 100644
index 000000000000..500ef54fd615
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-06-07-17-16-09.bpo-37178.Day_oB.rst
@@ -0,0 +1,2 @@
+Give math.perm() a one argument form that means the same as
+math.factorial().
diff --git a/Modules/clinic/mathmodule.c.h b/Modules/clinic/mathmodule.c.h
index cdf4305641b7..966b99b6a369 100644
--- a/Modules/clinic/mathmodule.c.h
+++ b/Modules/clinic/mathmodule.c.h
@@ -639,7 +639,7 @@ math_prod(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *k
 }
 
 PyDoc_STRVAR(math_perm__doc__,
-"perm($module, n, k, /)\n"
+"perm($module, n, k=None, /)\n"
 "--\n"
 "\n"
 "Number of ways to choose k items from n items without repetition and with order.\n"
@@ -647,6 +647,9 @@ PyDoc_STRVAR(math_perm__doc__,
 "Evaluates to n! / (n - k)! when k <= n and evaluates\n"
 "to zero when k > n.\n"
 "\n"
+"If k is not specified or is None, then k defaults to n\n"
+"and the function returns n!.\n"
+"\n"
 "Raises TypeError if either of the arguments are not integers.\n"
 "Raises ValueError if either of the arguments are negative.");
 
@@ -661,13 +664,17 @@ math_perm(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
 PyObject *return_value = NULL;
 PyObject *n;
- PyObject *k;
+ PyObject *k = Py_None;
 
- if (!_PyArg_CheckPositional("perm", nargs, 2, 2)) {
+ if (!_PyArg_CheckPositional("perm", nargs, 1, 2)) {
 goto exit;
 }
 n = args[0];
+ if (nargs < 2) {
+ goto skip_optional;
+ }
 k = args[1];
+skip_optional:
 return_value = math_perm_impl(module, n, k);
 
 exit:
@@ -713,4 +720,4 @@ math_comb(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 exit:
 return return_value;
 }
-/*[clinic end generated code: output=5004266613284dcc input=a9049054013a1b77]*/
+/*[clinic end generated code: output=0eb1e76a769cdd30 input=a9049054013a1b77]*/
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
index 9a9a8159ced4..ed1147675308 100644
--- a/Modules/mathmodule.c
+++ b/Modules/mathmodule.c
@@ -3002,7 +3002,7 @@ math_prod_impl(PyObject *module, PyObject *iterable, PyObject *start)
 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 @@ Number of ways to choose k items from n items without repetition and with order.
 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;
