Issue #23517: fromtimestamp() and utcfromtimestamp() methods of

datetime.datetime now round microseconds to nearest with ties going away from
zero (ROUND_HALF_UP), as Python 2 and Python older than 3.3, instead of
rounding towards -Infinity (ROUND_FLOOR).

2 files changed, 8 insertions, 7 deletions

diff --git a/Lib/datetime.py b/Lib/datetime.py
index d661460fa8..5ba2ddb7ab 100644
--- a/Lib/datetime.py
+++ b/Lib/datetime.py
@@ -1384,7 +1384,7 @@ class datetime(date):
         converter = _time.localtime if tz is None else _time.gmtime
 
         t, frac = divmod(t, 1.0)
-        us = int(frac * 1e6)
+        us = _round_half_up(frac * 1e6)
 
         # If timestamp is less than one microsecond smaller than a
         # full second, us can be rounded up to 1000000.  In this case,
@@ -1404,7 +1404,7 @@ class datetime(date):
     def utcfromtimestamp(cls, t):
         """Construct a naive UTC datetime from a POSIX timestamp."""
         t, frac = divmod(t, 1.0)
-        us = int(frac * 1e6)
+        us = _round_half_up(frac * 1e6)
 
         # If timestamp is less than one microsecond smaller than a
         # full second, us can be rounded up to 1000000.  In this case,
diff --git a/Lib/test/datetimetester.py b/Lib/test/datetimetester.py
index 62f55272d9..f516434bd6 100644
--- a/Lib/test/datetimetester.py
+++ b/Lib/test/datetimetester.py
@@ -1847,6 +1847,7 @@ class TestDateTime(TestDate):
             zero = fts(0)
             self.assertEqual(zero.second, 0)
             self.assertEqual(zero.microsecond, 0)
+            one = fts(1e-6)
             try:
                 minus_one = fts(-1e-6)
             except OSError:
@@ -1857,22 +1858,22 @@ class TestDateTime(TestDate):
                 self.assertEqual(minus_one.microsecond, 999999)
 
                 t = fts(-1e-8)
-                self.assertEqual(t, minus_one)
+                self.assertEqual(t, zero)
                 t = fts(-9e-7)
                 self.assertEqual(t, minus_one)
                 t = fts(-1e-7)
-                self.assertEqual(t, minus_one)
+                self.assertEqual(t, zero)
 
             t = fts(1e-7)
             self.assertEqual(t, zero)
             t = fts(9e-7)
-            self.assertEqual(t, zero)
+            self.assertEqual(t, one)
             t = fts(0.99999949)
             self.assertEqual(t.second, 0)
             self.assertEqual(t.microsecond, 999999)
             t = fts(0.9999999)
-            self.assertEqual(t.second, 0)
-            self.assertEqual(t.microsecond, 999999)
+            self.assertEqual(t.second, 1)
+            self.assertEqual(t.microsecond, 0)
 
     def test_insane_fromtimestamp(self):
         # It's possible that some platform maps time_t to double,