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Issue #23517: Fix rounding in fromtimestamp() and utcfromtimestamp() methods

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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.
This commit is contained in:
Victor Stinner 2015-09-18 14:42:05 +02:00
parent e3bcbd2bba
commit 511491ade0
4 changed files with 114 additions and 42 deletions
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24
Lib/test/datetimetester.py
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@ -650,8 +650,16 @@ class TestTimeDelta(HarmlessMixedComparison, unittest.TestCase):
# 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 @@ class TestDateTime(TestDate):
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 @@ 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(-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,