[Python-checkins] cpython (3.4): Issue #23517: Fix rounding in fromtimestamp() and utcfromtimestamp() methods
victor.stinner
python-checkins at python.org
Fri Sep 18 14:58:29 CEST 2015
https://hg.python.org/cpython/rev/ee1cf1b188d2
changeset: 98048:ee1cf1b188d2
branch: 3.4
parent: 98031:9f57c937958f
user: Victor Stinner <victor.stinner at gmail.com>
date: Fri Sep 18 14:42:05 2015 +0200
summary:
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.
files:
Lib/datetime.py | 53 ++++++++----------
Lib/test/datetimetester.py | 24 +++++++-
Misc/NEWS | 8 ++
Modules/_datetimemodule.c | 73 ++++++++++++++++++++++---
4 files changed, 115 insertions(+), 43 deletions(-)
diff --git a/Lib/datetime.py b/Lib/datetime.py
--- 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
--- 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,
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -81,6 +81,14 @@
Library
-------
+- 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.
+
- Issue #24684: socket.socket.getaddrinfo() now calls
PyUnicode_AsEncodedString() instead of calling the encode() method of the
host, to handle correctly custom string with an encode() method which doesn't
diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -4113,6 +4113,44 @@
tzinfo);
}
+static time_t
+_PyTime_DoubleToTimet(double x)
+{
+ time_t result;
+ double diff;
+
+ result = (time_t)x;
+ /* How much info did we lose? time_t may be an integral or
+ * floating type, and we don't know which. If it's integral,
+ * we don't know whether C truncates, rounds, returns the floor,
+ * etc. If we lost a second or more, the C rounding is
+ * unreasonable, or the input just doesn't fit in a time_t;
+ * call it an error regardless. Note that the original cast to
+ * time_t can cause a C error too, but nothing we can do to
+ * worm around that.
+ */
+ diff = x - (double)result;
+ if (diff <= -1.0 || diff >= 1.0) {
+ PyErr_SetString(PyExc_OverflowError,
+ "timestamp out of range for platform time_t");
+ result = (time_t)-1;
+ }
+ return result;
+}
+
+/* Round a double to the nearest long. |x| must be small enough to fit
+ * in a C long; this is not checked.
+ */
+static double
+_PyTime_RoundHalfEven(double x)
+{
+ double rounded = round(x);
+ if (fabs(x-rounded) == 0.5)
+ /* halfway case: round to even */
+ rounded = 2.0*round(x/2.0);
+ return rounded;
+}
+
/* Internal helper.
* Build datetime from a Python timestamp. Pass localtime or gmtime for f,
* to control the interpretation of the timestamp. Since a double doesn't
@@ -4121,15 +4159,32 @@
* to get that much precision (e.g., C time() isn't good enough).
*/
static PyObject *
-datetime_from_timestamp(PyObject *cls, TM_FUNC f, PyObject *timestamp,
+datetime_from_timestamp(PyObject *cls, TM_FUNC f, double timestamp,
PyObject *tzinfo)
{
time_t timet;
- long us;
-
- if (_PyTime_ObjectToTimeval(timestamp, &timet, &us, _PyTime_ROUND_DOWN) == -1)
+ double fraction;
+ int us;
+
+ timet = _PyTime_DoubleToTimet(timestamp);
+ if (timet == (time_t)-1 && PyErr_Occurred())
return NULL;
- return datetime_from_timet_and_us(cls, f, timet, (int)us, tzinfo);
+ fraction = timestamp - (double)timet;
+ us = (int)_PyTime_RoundHalfEven(fraction * 1e6);
+ if (us < 0) {
+ /* Truncation towards zero is not what we wanted
+ for negative numbers (Python's mod semantics) */
+ timet -= 1;
+ us += 1000000;
+ }
+ /* If timestamp is less than one microsecond smaller than a
+ * full second, round up. Otherwise, ValueErrors are raised
+ * for some floats. */
+ if (us == 1000000) {
+ timet += 1;
+ us = 0;
+ }
+ return datetime_from_timet_and_us(cls, f, timet, us, tzinfo);
}
/* Internal helper.
@@ -4231,11 +4286,11 @@
datetime_fromtimestamp(PyObject *cls, PyObject *args, PyObject *kw)
{
PyObject *self;
- PyObject *timestamp;
+ double timestamp;
PyObject *tzinfo = Py_None;
static char *keywords[] = {"timestamp", "tz", NULL};
- if (! PyArg_ParseTupleAndKeywords(args, kw, "O|O:fromtimestamp",
+ if (! PyArg_ParseTupleAndKeywords(args, kw, "d|O:fromtimestamp",
keywords, ×tamp, &tzinfo))
return NULL;
if (check_tzinfo_subclass(tzinfo) < 0)
@@ -4259,10 +4314,10 @@
static PyObject *
datetime_utcfromtimestamp(PyObject *cls, PyObject *args)
{
- PyObject *timestamp;
+ double timestamp;
PyObject *result = NULL;
- if (PyArg_ParseTuple(args, "O:utcfromtimestamp", ×tamp))
+ if (PyArg_ParseTuple(args, "d:utcfromtimestamp", ×tamp))
result = datetime_from_timestamp(cls, gmtime, timestamp,
Py_None);
return result;
--
Repository URL: https://hg.python.org/cpython
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