gh-91581: Check result of utc_to_seconds

Lib/datetime.py

@@ -1754,7 +1754,7 @@ def _fromtimestamp(cls, t, utc, tz):
         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)
-        if tz is None:
+        if tz is None and not utc:
             # As of version 2015f max fold in IANA database is
             # 23 hours at 1969-09-30 13:00:00 in Kwajalein.
             # Let's probe 24 hours in the past to detect a transition:
@@ -1775,7 +1775,7 @@ def _fromtimestamp(cls, t, utc, tz):
                 probe2 = cls(y, m, d, hh, mm, ss, us, tz)
                 if probe2 == result:
                     result._fold = 1
-        else:
+        elif tz is not None:
             result = tz.fromutc(result)
         return result
 

Lib/test/datetimetester.py

@@ -2515,45 +2515,101 @@ def test_microsecond_rounding(self):
             self.assertEqual(t.microsecond, 7812)
 
     def test_timestamp_limits(self):
-        # minimum timestamp
-        min_dt = self.theclass.min.replace(tzinfo=timezone.utc)
+        with self.subTest("minimum UTC"):
+            min_dt = self.theclass.min.replace(tzinfo=timezone.utc)
+            min_ts = min_dt.timestamp()
+
+            # This test assumes that datetime.min == 0000-01-01T00:00:00.00
+            # If that assumption changes, this value can change as well
+            self.assertEqual(min_ts, -62135596800)
+
+        with self.subTest("maximum UTC"):
+            # Zero out microseconds to avoid rounding issues
+            max_dt = self.theclass.max.replace(tzinfo=timezone.utc,
+                                               microsecond=0)
+            max_ts = max_dt.timestamp()
+
+            # This test assumes that datetime.max == 9999-12-31T23:59:59.999999
+            # If that assumption changes, this value can change as well
+            self.assertEqual(max_ts, 253402300799.0)
+
+    def test_fromtimestamp_limits(self):
+        try:
+            self.theclass.fromtimestamp(-2**32 - 1)
+        except (OSError, OverflowError):
+            self.skipTest("Test not valid on this platform")
+
+        # XXX: Replace these with datetime.{min,max}.timestamp() when we solve
+        # the issue with gh-91012
+        min_dt = self.theclass.min + timedelta(days=1)
         min_ts = min_dt.timestamp()
+
+        max_dt = self.theclass.max.replace(microsecond=0)
+        max_ts = ((self.theclass.max - timedelta(hours=23)).timestamp() +
+                  timedelta(hours=22, minutes=59, seconds=59).total_seconds())
+
+        for (test_name, ts, expected) in [
+                ("minimum", min_ts, min_dt),
+                ("maximum", max_ts, max_dt),
+        ]:
+            with self.subTest(test_name, ts=ts, expected=expected):
+                actual = self.theclass.fromtimestamp(ts)
+
+                self.assertEqual(actual, expected)
+
+        # Test error conditions
+        test_cases = [
+            ("Too small by a little", min_ts - timedelta(days=1, hours=12).total_seconds()),
+            ("Too small by a lot", min_ts - timedelta(days=400).total_seconds()),
+            ("Too big by a little", max_ts + timedelta(days=1).total_seconds()),
+            ("Too big by a lot", max_ts + timedelta(days=400).total_seconds()),
+        ]
+
+        for test_name, ts in test_cases:
+            with self.subTest(test_name, ts=ts):
+                with self.assertRaises((ValueError, OverflowError)):
+                    # converting a Python int to C time_t can raise a
+                    # OverflowError, especially on 32-bit platforms.
+                    self.theclass.fromtimestamp(ts)
+
+    def test_utcfromtimestamp_limits(self):
         try:
-            # date 0001-01-01 00:00:00+00:00: timestamp=-62135596800
-            self.assertEqual(self.theclass.fromtimestamp(min_ts, tz=timezone.utc),
-                             min_dt)
-        except (OverflowError, OSError) as exc:
-            # the date 0001-01-01 doesn't fit into 32-bit time_t,
-            # or platform doesn't support such very old date
-            self.skipTest(str(exc))
-
-        # maximum timestamp: set seconds to zero to avoid rounding issues
-        max_dt = self.theclass.max.replace(tzinfo=timezone.utc,
-                                           second=0, microsecond=0)
+            self.theclass.utcfromtimestamp(-2**32 - 1)
+        except (OSError, OverflowError):
+            self.skipTest("Test not valid on this platform")
+
+        min_dt = self.theclass.min.replace(tzinfo=timezone.utc)
+        min_ts = min_dt.timestamp()
+
+        max_dt = self.theclass.max.replace(microsecond=0, tzinfo=timezone.utc)
         max_ts = max_dt.timestamp()
-        # date 9999-12-31 23:59:00+00:00: timestamp 253402300740
-        self.assertEqual(self.theclass.fromtimestamp(max_ts, tz=timezone.utc),
-                         max_dt)
-
-        # number of seconds greater than 1 year: make sure that the new date
-        # is not valid in datetime.datetime limits
-        delta = 3600 * 24 * 400
-
-        # too small
-        ts = min_ts - delta
-        # converting a Python int to C time_t can raise a OverflowError,
-        # especially on 32-bit platforms.
-        with self.assertRaises((ValueError, OverflowError)):
-            self.theclass.fromtimestamp(ts)
-        with self.assertRaises((ValueError, OverflowError)):
-            self.theclass.utcfromtimestamp(ts)
-
-        # too big
-        ts = max_dt.timestamp() + delta
-        with self.assertRaises((ValueError, OverflowError)):
-            self.theclass.fromtimestamp(ts)
-        with self.assertRaises((ValueError, OverflowError)):
-            self.theclass.utcfromtimestamp(ts)
+
+        for (test_name, ts, expected) in [
+                ("minimum", min_ts, min_dt.replace(tzinfo=None)),
+                ("maximum", max_ts, max_dt.replace(tzinfo=None)),
+        ]:
+            with self.subTest(test_name, ts=ts, expected=expected):
+                try:
+                    actual = self.theclass.utcfromtimestamp(ts)
+                except (OSError, OverflowError) as exc:
+                    self.skipTest(str(exc))
+
+                self.assertEqual(actual, expected)
+
+        # Test error conditions
+        test_cases = [
+            ("Too small by a little", min_ts - 1),
+            ("Too small by a lot", min_ts - timedelta(days=400).total_seconds()),
+            ("Too big by a little", max_ts + 1),
+            ("Too big by a lot", max_ts + timedelta(days=400).total_seconds()),
+        ]
+
+        for test_name, ts in test_cases:
+            with self.subTest(test_name, ts=ts):
+                with self.assertRaises((ValueError, OverflowError)):
+                    # converting a Python int to C time_t can raise a
+                    # OverflowError, especially on 32-bit platforms.
+                    self.theclass.utcfromtimestamp(ts)
 
     def test_insane_fromtimestamp(self):
         # It's possible that some platform maps time_t to double,

Misc/NEWS.d/next/Library/2022-04-15-13-16-25.gh-issue-91581.9OGsrN.rst

@@ -0,0 +1,6 @@
+Remove an unhandled error case in the C implementation of calls to
+:meth:`datetime.fromtimestamp <datetime.datetime.fromtimestamp>` with no time
+zone (i.e. getting a local time from an epoch timestamp). This should have no
+user-facing effect other than giving a possibly more accurate error message
+when called with timestamps that fall on 10000-01-01 in the local time. Patch
+by Paul Ganssle.

Misc/NEWS.d/next/Library/2022-05-11-14-34-09.gh-issue-91581.glkou2.rst

@@ -0,0 +1,5 @@
+:meth:`~datetime.datetime.utcfromtimestamp` no longer attempts to resolve
+``fold`` in the pure Python implementation, since the fold is never 1 in UTC.
+In addition to being slightly faster in the common case, this also prevents
+some errors when the timestamp is close to :attr:`datetime.min
+<datetime.datetime.min>`.  Patch by Paul Ganssle.

Modules/_datetimemodule.c

@@ -5071,6 +5071,10 @@ datetime_from_timet_and_us(PyObject *cls, TM_FUNC f, time_t timet, int us,
 
         result_seconds = utc_to_seconds(year, month, day,
                                         hour, minute, second);
+        if (result_seconds == -1 && PyErr_Occurred()) {
+            return NULL;
+        }
+
         /* Probe max_fold_seconds to detect a fold. */
         probe_seconds = local(epoch + timet - max_fold_seconds);
         if (probe_seconds == -1)