May 21, 2025 · May 22, 2025
diff --git a/Lib/_pydatetime.py b/Lib/_pydatetime.py

 import time as _time
 import math as _math
 importsys
 importos
 from operator import index as _index

 def _cmp(x, y):
            # thus we can't perform fold detection for values of time less
            # than the max time fold. See comments in _datetimemodule's
            # version of this method for more details.
            if t < max_fold_seconds andsys.platform.startswith("win"):
            if t < max_fold_seconds andos.name == 'nt':
                return result

            y, m, d, hh, mm, ss = converter(t - max_fold_seconds)[:6]
    def timestamp(self):
        "Return POSIX timestamp as float"
        if self._tzinfo is None:
            if self < _NAIVE_EPOCH and os.name == 'nt':
                # Windows converters throw an OSError for negative values.
                return (self - _NAIVE_EPOCH).total_seconds()
            s = self._mktime()
            return s + self.microsecond / 1e6
        else:
 timezone.min = timezone._create(-timedelta(hours=23, minutes=59))
 timezone.max = timezone._create(timedelta(hours=23, minutes=59))
 _EPOCH = datetime(1970, 1, 1, tzinfo=timezone.utc)
 _NAIVE_EPOCH = datetime(1970, 1, 1)

 # Some time zone algebra.  For a datetime x, let
 #     x.n = x stripped of its timezone -- its naive time.
diff --git a/Lib/test/datetimetester.py b/Lib/test/datetimetester.py
        self.assertEqual(t.timestamp(),
                         18000 + 3600 + 2*60 + 3 + 4*1e-6)

    def test_naive_timestamp_before_epoch(self):
        # Before #81708 this raised OSError on Windows.
        self.assertLess(self.theclass(1969,1,1).timestamp(), 0)

    @support.run_with_tz('MSK-03')  # Something east of Greenwich
    def test_microsecond_rounding(self):
        def utcfromtimestamp(*args, **kwargs):
diff --git a/Misc/NEWS.d/next/Windows/2025-05-22-10-33-54.gh-issue-81708.xBa0wa.rst b/Misc/NEWS.d/next/Windows/2025-05-22-10-33-54.gh-issue-81708.xBa0wa.rst
 Support negative :meth:`datetime.datetime.timestamp` values from naive
 datetimes (before the UNIX epoch of 1970-01-01) on Windows by
 subtracting a naive epoch. Patch by John Keith Hohm.
diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
        result = delta_total_seconds(delta, NULL);
        Py_DECREF(delta);
    }
 #ifdef MS_WINDOWS
    else if (GET_YEAR(self) < 1970) {
        PyObject *naive_epoch = new_datetime(1970, 1, 1, 0, 0, 0, 0, Py_None, 0);
        if (naive_epoch == NULL) {
            return NULL;
        }
        PyObject *delta = datetime_subtract(op, naive_epoch);
        Py_DECREF(naive_epoch);
        if (delta == NULL)
            return NULL;
        result = delta_total_seconds(delta, NULL);
        Py_DECREF(delta);
    }
 #endif
    else {
        long long seconds;
        seconds = local_to_seconds(GET_YEAR(self),
Original file line number	Diff line number	Diff line change
Expand Up		@@ -8,7 +8,7 @@

		import time as _time
		import math as _math
		importsys
		importos
		from operator import index as _index

		def _cmp(x, y):
Expand DownExpand Up		@@ -1877,7 +1877,7 @@ def _fromtimestamp(cls, t, utc, tz):
		# thus we can't perform fold detection for values of time less
		# than the max time fold. See comments in _datetimemodule's
		# version of this method for more details.
		if t < max_fold_seconds andsys.platform.startswith("win"):
		if t < max_fold_seconds andos.name == 'nt':
		return result

		y, m, d, hh, mm, ss = converter(t - max_fold_seconds)[:6]
Expand DownExpand Up		@@ -2050,6 +2050,9 @@ def local(u):
		def timestamp(self):
		"Return POSIX timestamp as float"
		if self._tzinfo is None:
		if self < _NAIVE_EPOCH and os.name == 'nt':
		# Windows converters throw an OSError for negative values.
		return (self - _NAIVE_EPOCH).total_seconds()
		s = self._mktime()
		return s + self.microsecond / 1e6
		else:
Expand DownExpand Up		@@ -2561,6 +2564,7 @@ def _name_from_offset(delta):
		timezone.min = timezone._create(-timedelta(hours=23, minutes=59))
		timezone.max = timezone._create(timedelta(hours=23, minutes=59))
		_EPOCH = datetime(1970, 1, 1, tzinfo=timezone.utc)
		_NAIVE_EPOCH = datetime(1970, 1, 1)

		# Some time zone algebra. For a datetime x, let
		# x.n = x stripped of its timezone -- its naive time.
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -2671,6 +2671,10 @@ def test_timestamp_aware(self):
		self.assertEqual(t.timestamp(),
		18000 + 3600 + 260 + 3 + 41e-6)

		def test_naive_timestamp_before_epoch(self):
		# Before #81708 this raised OSError on Windows.
		self.assertLess(self.theclass(1969,1,1).timestamp(), 0)

		@support.run_with_tz('MSK-03') # Something east of Greenwich
		def test_microsecond_rounding(self):
		def utcfromtimestamp(args, *kwargs):
Expand Down
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,3 @@
		Support negative :meth:`datetime.datetime.timestamp` values from naive
		datetimes (before the UNIX epoch of 1970-01-01) on Windows by
		subtracting a naive epoch. Patch by John Keith Hohm.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -6869,6 +6869,20 @@ datetime_timestamp(PyObject op, PyObject Py_UNUSED(dummy))
		result = delta_total_seconds(delta, NULL);
		Py_DECREF(delta);
		}
		#ifdef MS_WINDOWS
		else if (GET_YEAR(self) < 1970) {
		PyObject *naive_epoch = new_datetime(1970, 1, 1, 0, 0, 0, 0, Py_None, 0);
		if (naive_epoch == NULL) {
		return NULL;
		}
		PyObject *delta = datetime_subtract(op, naive_epoch);
		Py_DECREF(naive_epoch);
		if (delta == NULL)
		return NULL;
		result = delta_total_seconds(delta, NULL);
		Py_DECREF(delta);
		}
		#endif
		else {
		long long seconds;
		seconds = local_to_seconds(GET_YEAR(self),
Expand Down