Issue #23517: Fix rounding in fromtimestamp() and utcfromtimestamp() methods
of datetime.datetime: microseconds are now rounded to nearest with ties going
to nearest even integer (ROUND_HALF_EVEN), instead of being rounding towards
zero (ROUND_DOWN). It's important that these methods use the same rounding
mode than datetime.timedelta to keep the property:
(datetime(1970,1,1) + timedelta(seconds=t)) == datetime.utcfromtimestamp(t)
It also the rounding mode used by round(float) for example.
Add more unit tests on the rounding mode in test_datetime.
diff --git a/Lib/datetime.py b/Lib/datetime.py
index 34e5d38..3af12e7 100644
--- a/Lib/datetime.py
+++ b/Lib/datetime.py
@@ -1362,49 +1362,42 @@
return self._tzinfo
@classmethod
+ def _fromtimestamp(cls, t, utc, tz):
+ """Construct a datetime from a POSIX timestamp (like time.time()).
+
+ A timezone info object may be passed in as well.
+ """
+ frac, t = _math.modf(t)
+ us = round(frac * 1e6)
+ if us >= 1000000:
+ t += 1
+ us -= 1000000
+ elif us < 0:
+ t -= 1
+ us += 1000000
+
+ converter = _time.gmtime if utc else _time.localtime
+ y, m, d, hh, mm, ss, weekday, jday, dst = converter(t)
+ ss = min(ss, 59) # clamp out leap seconds if the platform has them
+ return cls(y, m, d, hh, mm, ss, us, tz)
+
+ @classmethod
def fromtimestamp(cls, t, tz=None):
"""Construct a datetime from a POSIX timestamp (like time.time()).
A timezone info object may be passed in as well.
"""
-
_check_tzinfo_arg(tz)
- converter = _time.localtime if tz is None else _time.gmtime
-
- t, frac = divmod(t, 1.0)
- us = int(frac * 1e6)
-
- # If timestamp is less than one microsecond smaller than a
- # full second, us can be rounded up to 1000000. In this case,
- # roll over to seconds, otherwise, ValueError is raised
- # by the constructor.
- if us == 1000000:
- t += 1
- us = 0
- y, m, d, hh, mm, ss, weekday, jday, dst = converter(t)
- ss = min(ss, 59) # clamp out leap seconds if the platform has them
- result = cls(y, m, d, hh, mm, ss, us, tz)
+ result = cls._fromtimestamp(t, tz is not None, tz)
if tz is not None:
result = tz.fromutc(result)
return result
@classmethod
def utcfromtimestamp(cls, t):
- "Construct a UTC datetime from a POSIX timestamp (like time.time())."
- t, frac = divmod(t, 1.0)
- us = int(frac * 1e6)
-
- # If timestamp is less than one microsecond smaller than a
- # full second, us can be rounded up to 1000000. In this case,
- # roll over to seconds, otherwise, ValueError is raised
- # by the constructor.
- if us == 1000000:
- t += 1
- us = 0
- y, m, d, hh, mm, ss, weekday, jday, dst = _time.gmtime(t)
- ss = min(ss, 59) # clamp out leap seconds if the platform has them
- return cls(y, m, d, hh, mm, ss, us)
+ """Construct a naive UTC datetime from a POSIX timestamp."""
+ return cls._fromtimestamp(t, True, None)
# XXX This is supposed to do better than we *can* do by using time.time(),
# XXX if the platform supports a more accurate way. The C implementation
diff --git a/Lib/test/datetimetester.py b/Lib/test/datetimetester.py
index 8e48b9f..a942d4d 100644
--- a/Lib/test/datetimetester.py
+++ b/Lib/test/datetimetester.py
@@ -650,8 +650,16 @@
# Single-field rounding.
eq(td(milliseconds=0.4/1000), td(0)) # rounds to 0
eq(td(milliseconds=-0.4/1000), td(0)) # rounds to 0
+ eq(td(milliseconds=0.5/1000), td(microseconds=0))
+ eq(td(milliseconds=-0.5/1000), td(microseconds=-0))
eq(td(milliseconds=0.6/1000), td(microseconds=1))
eq(td(milliseconds=-0.6/1000), td(microseconds=-1))
+ eq(td(milliseconds=1.5/1000), td(microseconds=2))
+ eq(td(milliseconds=-1.5/1000), td(microseconds=-2))
+ eq(td(seconds=0.5/10**6), td(microseconds=0))
+ eq(td(seconds=-0.5/10**6), td(microseconds=-0))
+ eq(td(seconds=1/2**7), td(microseconds=7812))
+ eq(td(seconds=-1/2**7), td(microseconds=-7812))
# Rounding due to contributions from more than one field.
us_per_hour = 3600e6
@@ -1824,12 +1832,14 @@
tzinfo=timezone(timedelta(hours=-5), 'EST'))
self.assertEqual(t.timestamp(),
18000 + 3600 + 2*60 + 3 + 4*1e-6)
+
def test_microsecond_rounding(self):
for fts in [self.theclass.fromtimestamp,
self.theclass.utcfromtimestamp]:
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:
@@ -1840,22 +1850,28 @@
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(-1/2**7)
+ self.assertEqual(t.second, 59)
+ self.assertEqual(t.microsecond, 992188)
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, 1)
+ self.assertEqual(t.microsecond, 0)
+ t = fts(1/2**7)
self.assertEqual(t.second, 0)
- self.assertEqual(t.microsecond, 999999)
+ self.assertEqual(t.microsecond, 7812)
def test_insane_fromtimestamp(self):
# It's possible that some platform maps time_t to double,