Issue #4707: round(x, n) now returns an integer when x is an integer.

Previously it returned a float.

2 files changed, 78 insertions, 3 deletions

diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index 99785dc..284f07e 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -1068,9 +1068,9 @@ class BuiltinTest(unittest.TestCase):
         self.assertEqual(round(8), 8)
         self.assertEqual(round(-8), -8)
         self.assertEqual(type(round(0)), int)
-        self.assertEqual(type(round(-8, -1)), float)
-        self.assertEqual(type(round(-8, 0)), float)
-        self.assertEqual(type(round(-8, 1)), float)
+        self.assertEqual(type(round(-8, -1)), int)
+        self.assertEqual(type(round(-8, 0)), int)
+        self.assertEqual(type(round(-8, 1)), int)
 
         # test new kwargs
         self.assertEqual(round(number=-8.0, ndigits=-1), -10.0)
diff --git a/Lib/test/test_long.py b/Lib/test/test_long.py
index 2acb3fa..0e07090 100644
--- a/Lib/test/test_long.py
+++ b/Lib/test/test_long.py
@@ -896,6 +896,81 @@ class LongTest(unittest.TestCase):
             self.assertEqual((a+1).bit_length(), i+1)
             self.assertEqual((-a-1).bit_length(), i+1)
 
+    def test_round(self):
+        # check round-half-even algorithm. For round to nearest ten;
+        # rounding map is invariant under adding multiples of 20
+        test_dict = {0:0, 1:0, 2:0, 3:0, 4:0, 5:0,
+                     6:10, 7:10, 8:10, 9:10, 10:10, 11:10, 12:10, 13:10, 14:10,
+                     15:20, 16:20, 17:20, 18:20, 19:20}
+        for offset in range(-520, 520, 20):
+            for k, v in test_dict.items():
+                got = round(k+offset, -1)
+                expected = v+offset
+                self.assertEqual(got, expected)
+                self.assert_(type(got) is int)
+
+        # larger second argument
+        self.assertEqual(round(-150, -2), -200)
+        self.assertEqual(round(-149, -2), -100)
+        self.assertEqual(round(-51, -2), -100)
+        self.assertEqual(round(-50, -2), 0)
+        self.assertEqual(round(-49, -2), 0)
+        self.assertEqual(round(-1, -2), 0)
+        self.assertEqual(round(0, -2), 0)
+        self.assertEqual(round(1, -2), 0)
+        self.assertEqual(round(49, -2), 0)
+        self.assertEqual(round(50, -2), 0)
+        self.assertEqual(round(51, -2), 100)
+        self.assertEqual(round(149, -2), 100)
+        self.assertEqual(round(150, -2), 200)
+        self.assertEqual(round(250, -2), 200)
+        self.assertEqual(round(251, -2), 300)
+        self.assertEqual(round(172500, -3), 172000)
+        self.assertEqual(round(173500, -3), 174000)
+        self.assertEqual(round(31415926535, -1), 31415926540)
+        self.assertEqual(round(31415926535, -2), 31415926500)
+        self.assertEqual(round(31415926535, -3), 31415927000)
+        self.assertEqual(round(31415926535, -4), 31415930000)
+        self.assertEqual(round(31415926535, -5), 31415900000)
+        self.assertEqual(round(31415926535, -6), 31416000000)
+        self.assertEqual(round(31415926535, -7), 31420000000)
+        self.assertEqual(round(31415926535, -8), 31400000000)
+        self.assertEqual(round(31415926535, -9), 31000000000)
+        self.assertEqual(round(31415926535, -10), 30000000000)
+        self.assertEqual(round(31415926535, -11), 0)
+        self.assertEqual(round(31415926535, -12), 0)
+        self.assertEqual(round(31415926535, -999), 0)
+
+        # should get correct results even for huge inputs
+        for k in range(10, 100):
+            got = round(10**k + 324678, -3)
+            expect = 10**k + 325000
+            self.assertEqual(got, expect)
+            self.assert_(type(got) is int)
+
+        # nonnegative second argument: round(x, n) should just return x
+        for n in range(5):
+            for i in range(100):
+                x = random.randrange(-10000, 10000)
+                got = round(x, n)
+                self.assertEqual(got, x)
+                self.assert_(type(got) is int)
+        for huge_n in 2**31-1, 2**31, 2**63-1, 2**63, 2**100, 10**100:
+            self.assertEqual(round(8979323, huge_n), 8979323)
+
+        # omitted second argument
+        for i in range(100):
+            x = random.randrange(-10000, 10000)
+            got = round(x)
+            self.assertEqual(got, x)
+            self.assert_(type(got) is int)
+
+        # bad second argument
+        bad_exponents = ('brian', 2.0, 0j, None)
+        for e in bad_exponents:
+            self.assertRaises(TypeError, round, 3, e)
+
+
 
 def test_main():
     support.run_unittest(LongTest)