bpo-37128: Add math.perm(). (GH-13731)

1 files changed, 65 insertions, 1 deletions

diff --git a/Lib/test/test_math.py b/Lib/test/test_math.py
index e27092e..96e0cf2 100644
--- a/Lib/test/test_math.py
+++ b/Lib/test/test_math.py
@@ -240,6 +240,9 @@ def result_check(expected, got, ulp_tol=5, abs_tol=0.0):
     else:
         return None
 
+class IntSubclass(int):
+    pass
+
 # Class providing an __index__ method.
 class MyIndexable(object):
     def __init__(self, value):
@@ -1862,6 +1865,64 @@ class IsCloseTests(unittest.TestCase):
         self.assertAllClose(fraction_examples, rel_tol=1e-8)
         self.assertAllNotClose(fraction_examples, rel_tol=1e-9)
 
+    def testPerm(self):
+        perm = math.perm
+        factorial = math.factorial
+        # Test if factorial defintion is satisfied
+        for n in range(100):
+            for k in range(n + 1):
+                self.assertEqual(perm(n, k),
+                                 factorial(n) // factorial(n - k))
+
+        # Test for Pascal's identity
+        for n in range(1, 100):
+            for k in range(1, n):
+                self.assertEqual(perm(n, k), perm(n - 1, k - 1) * k + perm(n - 1, k))
+
+        # Test corner cases
+        for n in range(1, 100):
+            self.assertEqual(perm(n, 0), 1)
+            self.assertEqual(perm(n, 1), n)
+            self.assertEqual(perm(n, n), factorial(n))
+
+        # Raises TypeError if any argument is non-integer or argument count is
+        # not 2
+        self.assertRaises(TypeError, perm, 10, 1.0)
+        self.assertRaises(TypeError, perm, 10, decimal.Decimal(1.0))
+        self.assertRaises(TypeError, perm, 10, "1")
+        self.assertRaises(TypeError, perm, 10.0, 1)
+        self.assertRaises(TypeError, perm, decimal.Decimal(10.0), 1)
+        self.assertRaises(TypeError, perm, "10", 1)
+
+        self.assertRaises(TypeError, perm, 10)
+        self.assertRaises(TypeError, perm, 10, 1, 3)
+        self.assertRaises(TypeError, perm)
+
+        # Raises Value error if not k or n are negative numbers
+        self.assertRaises(ValueError, perm, -1, 1)
+        self.assertRaises(ValueError, perm, -2**1000, 1)
+        self.assertRaises(ValueError, perm, 1, -1)
+        self.assertRaises(ValueError, perm, 1, -2**1000)
+
+        # Raises value error if k is greater than n
+        self.assertRaises(ValueError, perm, 1, 2)
+        self.assertRaises(ValueError, perm, 1, 2**1000)
+
+        n = 2**1000
+        self.assertEqual(perm(n, 0), 1)
+        self.assertEqual(perm(n, 1), n)
+        self.assertEqual(perm(n, 2), n * (n-1))
+        self.assertRaises((OverflowError, MemoryError), perm, n, n)
+
+        for n, k in (True, True), (True, False), (False, False):
+            self.assertEqual(perm(n, k), 1)
+            self.assertIs(type(perm(n, k)), int)
+        self.assertEqual(perm(IntSubclass(5), IntSubclass(2)), 20)
+        self.assertEqual(perm(MyIndexable(5), MyIndexable(2)), 20)
+        for k in range(3):
+            self.assertIs(type(perm(IntSubclass(5), IntSubclass(k))), int)
+            self.assertIs(type(perm(MyIndexable(5), MyIndexable(k))), int)
+
     def testComb(self):
         comb = math.comb
         factorial = math.factorial
@@ -1925,8 +1986,11 @@ class IsCloseTests(unittest.TestCase):
         for n, k in (True, True), (True, False), (False, False):
             self.assertEqual(comb(n, k), 1)
             self.assertIs(type(comb(n, k)), int)
+        self.assertEqual(comb(IntSubclass(5), IntSubclass(2)), 10)
         self.assertEqual(comb(MyIndexable(5), MyIndexable(2)), 10)
-        self.assertIs(type(comb(MyIndexable(5), MyIndexable(2))), int)
+        for k in range(3):
+            self.assertIs(type(comb(IntSubclass(5), IntSubclass(k))), int)
+            self.assertIs(type(comb(MyIndexable(5), MyIndexable(k))), int)
 
 
 def test_main():