bpo-37178: Allow a one argument form of math.perm() (GH-13905)

This commit is contained in:
Raymond Hettinger 2019-06-08 08:58:11 -07:00 committed by GitHub
parent 8cc605acdd
commit e119b3d136
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
6 changed files with 34 additions and 9 deletions

View File

@ -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.

View File

@ -1885,8 +1885,13 @@ class IsCloseTests(unittest.TestCase):
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 @@ class IsCloseTests(unittest.TestCase):
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)

View File

@ -0,0 +1,2 @@
For math.perm(n, k), let k default to n, giving the same result as
factorial.

View File

@ -0,0 +1,2 @@
Give math.perm() a one argument form that means the same as
math.factorial().

View File

@ -639,7 +639,7 @@ exit:
}
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]*/

View File

@ -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;