bpo-37642: Update acceptable offsets in timezone (GH-14878)

This fixes an inconsistency between the Python and C implementations of
the datetime module. The pure python version of the code was not
accepting offsets greater than 23:59 but less than 24:00. This is an
accidental legacy of the original implementation, which was put in place
before tzinfo allowed sub-minute time zone offsets.

GH-14878

5 files changed, 44 insertions, 5 deletions

diff --git a/Lib/datetime.py b/Lib/datetime.py
index d4c7a1f..0adf1dd 100644
--- a/Lib/datetime.py
+++ b/Lib/datetime.py
@@ -2269,7 +2269,7 @@ class timezone(tzinfo):
         raise TypeError("fromutc() argument must be a datetime instance"
                         " or None")
 
-    _maxoffset = timedelta(hours=23, minutes=59)
+    _maxoffset = timedelta(hours=24, microseconds=-1)
     _minoffset = -_maxoffset
 
     @staticmethod
@@ -2293,8 +2293,11 @@ class timezone(tzinfo):
         return f'UTC{sign}{hours:02d}:{minutes:02d}'
 
 timezone.utc = timezone._create(timedelta(0))
-timezone.min = timezone._create(timezone._minoffset)
-timezone.max = timezone._create(timezone._maxoffset)
+# bpo-37642: These attributes are rounded to the nearest minute for backwards
+# compatibility, even though the constructor will accept a wider range of
+# values. This may change in the future.
+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)
 
 # Some time zone algebra.  For a datetime x, let
diff --git a/Lib/test/datetimetester.py b/Lib/test/datetimetester.py
index 99b620c..d0101c9 100644
--- a/Lib/test/datetimetester.py
+++ b/Lib/test/datetimetester.py
@@ -388,6 +388,31 @@ class TestTimeZone(unittest.TestCase):
         tz_copy = copy.deepcopy(tz)
         self.assertIs(tz_copy, tz)
 
+    def test_offset_boundaries(self):
+        # Test timedeltas close to the boundaries
+        time_deltas = [
+            timedelta(hours=23, minutes=59),
+            timedelta(hours=23, minutes=59, seconds=59),
+            timedelta(hours=23, minutes=59, seconds=59, microseconds=999999),
+        ]
+        time_deltas.extend([-delta for delta in time_deltas])
+
+        for delta in time_deltas:
+            with self.subTest(test_type='good', delta=delta):
+                timezone(delta)
+
+        # Test timedeltas on and outside the boundaries
+        bad_time_deltas = [
+            timedelta(hours=24),
+            timedelta(hours=24, microseconds=1),
+        ]
+        bad_time_deltas.extend([-delta for delta in bad_time_deltas])
+
+        for delta in bad_time_deltas:
+            with self.subTest(test_type='bad', delta=delta):
+                with self.assertRaises(ValueError):
+                    timezone(delta)
+
 
 #############################################################################
 # Base class for testing a particular aspect of timedelta, time, date and
diff --git a/Misc/ACKS b/Misc/ACKS
index 8c834b4..3b4cf85 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1881,3 +1881,4 @@ Aleksandr Balezin
 Robert Leenders
 Tim Hopper
 Dan Lidral-Porter
+Ngalim Siregar
diff --git a/Misc/NEWS.d/next/Library/2019-07-21-20-59-31.bpo-37642.L61Bvy.rst b/Misc/NEWS.d/next/Library/2019-07-21-20-59-31.bpo-37642.L61Bvy.rst
new file mode 100644
index 0000000..09ff257
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-07-21-20-59-31.bpo-37642.L61Bvy.rst
@@ -0,0 +1,3 @@
+Allowed the pure Python implementation of :class:`datetime.timezone` to represent
+sub-minute offsets close to minimum and maximum boundaries, specifically in the
+ranges (23:59, 24:00) and (-23:59, 24:00). Patch by Ngalim Siregar
diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index b55922c..6d28b3e 100644
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -1099,7 +1099,9 @@ new_timezone(PyObject *offset, PyObject *name)
         Py_INCREF(PyDateTime_TimeZone_UTC);
         return PyDateTime_TimeZone_UTC;
     }
-    if ((GET_TD_DAYS(offset) == -1 && GET_TD_SECONDS(offset) == 0) ||
+    if ((GET_TD_DAYS(offset) == -1 &&
+            GET_TD_SECONDS(offset) == 0 &&
+            GET_TD_MICROSECONDS(offset) < 1) ||
         GET_TD_DAYS(offset) < -1 || GET_TD_DAYS(offset) >= 1) {
         PyErr_Format(PyExc_ValueError, "offset must be a timedelta"
                      " strictly between -timedelta(hours=24) and"
@@ -1169,7 +1171,9 @@ call_tzinfo_method(PyObject *tzinfo, const char *name, PyObject *tzinfoarg)
     if (offset == Py_None || offset == NULL)
         return offset;
     if (PyDelta_Check(offset)) {
-        if ((GET_TD_DAYS(offset) == -1 && GET_TD_SECONDS(offset) == 0) ||
+        if ((GET_TD_DAYS(offset) == -1 &&
+                GET_TD_SECONDS(offset) == 0 &&
+                GET_TD_MICROSECONDS(offset) < 1) ||
             GET_TD_DAYS(offset) < -1 || GET_TD_DAYS(offset) >= 1) {
             Py_DECREF(offset);
             PyErr_Format(PyExc_ValueError, "offset must be a timedelta"
@@ -6481,6 +6485,9 @@ PyInit__datetime(void)
     PyDateTime_TimeZone_UTC = x;
     CAPI.TimeZone_UTC = PyDateTime_TimeZone_UTC;
 
+    /* bpo-37642: These attributes are rounded to the nearest minute for backwards
+     * compatibility, even though the constructor will accept a wider range of
+     * values. This may change in the future.*/
     delta = new_delta(-1, 60, 0, 1); /* -23:59 */
     if (delta == NULL)
         return NULL;