bpo-37685: Fixed comparisons of datetime.timedelta and datetime.timezone. (GH-14996)

There was a discrepancy between the Python and C implementations.

Add singletons ALWAYS_EQ, LARGEST and SMALLEST in test.support
to test mixed type comparison.

Author: serhiy-storchaka

Doc/library/test.rst

@@ -356,11 +356,28 @@ The :mod:`test.support` module defines the following constants:
 
    Check for presence of docstrings.
 
+
 .. data:: TEST_HTTP_URL
 
    Define the URL of a dedicated HTTP server for the network tests.
 
 
+.. data:: ALWAYS_EQ
+
+   Object that is equal to anything.  Used to test mixed type comparison.
+
+
+.. data:: LARGEST
+
+   Object that is greater than anything (except itself).
+   Used to test mixed type comparison.
+
+
+.. data:: SMALLEST
+
+   Object that is less than anything (except itself).
+   Used to test mixed type comparison.
+
 
 The :mod:`test.support` module defines the following functions:
 

Lib/datetime.py

@@ -739,25 +739,25 @@ def __le__(self, other):
         if isinstance(other, timedelta):
             return self._cmp(other) <= 0
         else:
-            _cmperror(self, other)
+            return NotImplemented
 
     def __lt__(self, other):
         if isinstance(other, timedelta):
             return self._cmp(other) < 0
         else:
-            _cmperror(self, other)
+            return NotImplemented
 
     def __ge__(self, other):
         if isinstance(other, timedelta):
             return self._cmp(other) >= 0
         else:
-            _cmperror(self, other)
+            return NotImplemented
 
     def __gt__(self, other):
         if isinstance(other, timedelta):
             return self._cmp(other) > 0
         else:
-            _cmperror(self, other)
+            return NotImplemented
 
     def _cmp(self, other):
         assert isinstance(other, timedelta)
@@ -1316,25 +1316,25 @@ def __le__(self, other):
         if isinstance(other, time):
             return self._cmp(other) <= 0
         else:
-            _cmperror(self, other)
+            return NotImplemented
 
     def __lt__(self, other):
         if isinstance(other, time):
             return self._cmp(other) < 0
         else:
-            _cmperror(self, other)
+            return NotImplemented
 
     def __ge__(self, other):
         if isinstance(other, time):
             return self._cmp(other) >= 0
         else:
-            _cmperror(self, other)
+            return NotImplemented
 
     def __gt__(self, other):
         if isinstance(other, time):
             return self._cmp(other) > 0
         else:
-            _cmperror(self, other)
+            return NotImplemented
 
     def _cmp(self, other, allow_mixed=False):
         assert isinstance(other, time)
@@ -2210,9 +2210,9 @@ def __getinitargs__(self):
         return (self._offset, self._name)
 
     def __eq__(self, other):
-        if type(other) != timezone:
-            return False
-        return self._offset == other._offset
+        if isinstance(other, timezone):
+            return self._offset == other._offset
+        return NotImplemented
 
     def __hash__(self):
         return hash(self._offset)

Lib/test/datetimetester.py

@@ -2,11 +2,8 @@
 
 See http://www.zope.org/Members/fdrake/DateTimeWiki/TestCases
 """
-from test.support import is_resource_enabled
-
 import itertools
 import bisect
-
 import copy
 import decimal
 import sys
@@ -22,6 +19,7 @@
 from operator import lt, le, gt, ge, eq, ne, truediv, floordiv, mod
 
 from test import support
+from test.support import is_resource_enabled, ALWAYS_EQ, LARGEST, SMALLEST
 
 import datetime as datetime_module
 from datetime import MINYEAR, MAXYEAR
@@ -54,18 +52,6 @@
 NAN = float("nan")
 
 
-class ComparesEqualClass(object):
-    """
-    A class that is always equal to whatever you compare it to.
-    """
-
-    def __eq__(self, other):
-        return True
-
-    def __ne__(self, other):
-        return False
-
-
 #############################################################################
 # module tests
 
@@ -353,6 +339,18 @@ def test_comparison(self):
         self.assertTrue(timezone(ZERO) != None)
         self.assertFalse(timezone(ZERO) ==  None)
 
+        tz = timezone(ZERO)
+        self.assertTrue(tz == ALWAYS_EQ)
+        self.assertFalse(tz != ALWAYS_EQ)
+        self.assertTrue(tz < LARGEST)
+        self.assertFalse(tz > LARGEST)
+        self.assertTrue(tz <= LARGEST)
+        self.assertFalse(tz >= LARGEST)
+        self.assertFalse(tz < SMALLEST)
+        self.assertTrue(tz > SMALLEST)
+        self.assertFalse(tz <= SMALLEST)
+        self.assertTrue(tz >= SMALLEST)
+
     def test_aware_datetime(self):
         # test that timezone instances can be used by datetime
         t = datetime(1, 1, 1)
@@ -414,10 +412,21 @@ def test_harmless_mixed_comparison(self):
 
         # Comparison to objects of unsupported types should return
         # NotImplemented which falls back to the right hand side's __eq__
-        # method. In this case, ComparesEqualClass.__eq__ always returns True.
-        # ComparesEqualClass.__ne__ always returns False.
-        self.assertTrue(me == ComparesEqualClass())
-        self.assertFalse(me != ComparesEqualClass())
+        # method. In this case, ALWAYS_EQ.__eq__ always returns True.
+        # ALWAYS_EQ.__ne__ always returns False.
+        self.assertTrue(me == ALWAYS_EQ)
+        self.assertFalse(me != ALWAYS_EQ)
+
+        # If the other class explicitly defines ordering
+        # relative to our class, it is allowed to do so
+        self.assertTrue(me < LARGEST)
+        self.assertFalse(me > LARGEST)
+        self.assertTrue(me <= LARGEST)
+        self.assertFalse(me >= LARGEST)
+        self.assertFalse(me < SMALLEST)
+        self.assertTrue(me > SMALLEST)
+        self.assertFalse(me <= SMALLEST)
+        self.assertTrue(me >= SMALLEST)
 
     def test_harmful_mixed_comparison(self):
         me = self.theclass(1, 1, 1)
@@ -1582,29 +1591,6 @@ class SomeClass:
         self.assertRaises(TypeError, lambda: our < their)
         self.assertRaises(TypeError, lambda: their < our)
 
-        # However, if the other class explicitly defines ordering
-        # relative to our class, it is allowed to do so
-
-        class LargerThanAnything:
-            def __lt__(self, other):
-                return False
-            def __le__(self, other):
-                return isinstance(other, LargerThanAnything)
-            def __eq__(self, other):
-                return isinstance(other, LargerThanAnything)
-            def __gt__(self, other):
-                return not isinstance(other, LargerThanAnything)
-            def __ge__(self, other):
-                return True
-
-        their = LargerThanAnything()
-        self.assertEqual(our == their, False)
-        self.assertEqual(their == our, False)
-        self.assertEqual(our != their, True)
-        self.assertEqual(their != our, True)
-        self.assertEqual(our < their, True)
-        self.assertEqual(their < our, False)
-
     def test_bool(self):
         # All dates are considered true.
         self.assertTrue(self.theclass.min)
@@ -3781,8 +3767,8 @@ def test_replace(self):
         self.assertRaises(ValueError, base.replace, microsecond=1000000)
 
     def test_mixed_compare(self):
-        t1 = time(1, 2, 3)
-        t2 = time(1, 2, 3)
+        t1 = self.theclass(1, 2, 3)
+        t2 = self.theclass(1, 2, 3)
         self.assertEqual(t1, t2)
         t2 = t2.replace(tzinfo=None)
         self.assertEqual(t1, t2)

Lib/test/support/__init__.py

@@ -113,6 +113,7 @@
     "run_with_locale", "swap_item",
     "swap_attr", "Matcher", "set_memlimit", "SuppressCrashReport", "sortdict",
     "run_with_tz", "PGO", "missing_compiler_executable", "fd_count",
+    "ALWAYS_EQ", "LARGEST", "SMALLEST"
     ]
 
 class Error(Exception):
@@ -3103,6 +3104,41 @@ def __fspath__(self):
             return self.path
 
 
+class _ALWAYS_EQ:
+    """
+    Object that is equal to anything.
+    """
+    def __eq__(self, other):
+        return True
+    def __ne__(self, other):
+        return False
+
+ALWAYS_EQ = _ALWAYS_EQ()
+
+@functools.total_ordering
+class _LARGEST:
+    """
+    Object that is greater than anything (except itself).
+    """
+    def __eq__(self, other):
+        return isinstance(other, _LARGEST)
+    def __lt__(self, other):
+        return False
+
+LARGEST = _LARGEST()
+
+@functools.total_ordering
+class _SMALLEST:
+    """
+    Object that is less than anything (except itself).
+    """
+    def __eq__(self, other):
+        return isinstance(other, _SMALLEST)
+    def __gt__(self, other):
+        return False
+
+SMALLEST = _SMALLEST()
+
 def maybe_get_event_loop_policy():
     """Return the global event loop policy if one is set, else return None."""
     return asyncio.events._event_loop_policy

Lib/test/test_ipaddress.py

@@ -12,6 +12,7 @@
 import pickle
 import ipaddress
 import weakref
+from test.support import LARGEST, SMALLEST
 
 
 class BaseTestCase(unittest.TestCase):
@@ -673,20 +674,6 @@ def test_ip_network(self):
         self.assertFactoryError(ipaddress.ip_network, "network")
 
 
-@functools.total_ordering
-class LargestObject:
-    def __eq__(self, other):
-        return isinstance(other, LargestObject)
-    def __lt__(self, other):
-        return False
-
-@functools.total_ordering
-class SmallestObject:
-    def __eq__(self, other):
-        return isinstance(other, SmallestObject)
-    def __gt__(self, other):
-        return False
-
 class ComparisonTests(unittest.TestCase):
 
     v4addr = ipaddress.IPv4Address(1)
@@ -775,8 +762,6 @@ def test_mixed_type_ordering(self):
 
     def test_foreign_type_ordering(self):
         other = object()
-        smallest = SmallestObject()
-        largest = LargestObject()
         for obj in self.objects:
             with self.assertRaises(TypeError):
                 obj < other
@@ -786,14 +771,14 @@ def test_foreign_type_ordering(self):
                 obj <= other
             with self.assertRaises(TypeError):
                 obj >= other
-            self.assertTrue(obj < largest)
-            self.assertFalse(obj > largest)
-            self.assertTrue(obj <= largest)
-            self.assertFalse(obj >= largest)
-            self.assertFalse(obj < smallest)
-            self.assertTrue(obj > smallest)
-            self.assertFalse(obj <= smallest)
-            self.assertTrue(obj >= smallest)
+            self.assertTrue(obj < LARGEST)
+            self.assertFalse(obj > LARGEST)
+            self.assertTrue(obj <= LARGEST)
+            self.assertFalse(obj >= LARGEST)
+            self.assertFalse(obj < SMALLEST)
+            self.assertTrue(obj > SMALLEST)
+            self.assertFalse(obj <= SMALLEST)
+            self.assertTrue(obj >= SMALLEST)
 
     def test_mixed_type_key(self):
         # with get_mixed_type_key, you can sort addresses and network.

Misc/NEWS.d/next/Library/2019-07-28-22-25-25.bpo-37685._3bN9f.rst

@@ -0,0 +1,2 @@
+Fixed comparisons of :class:`datetime.timedelta` and
+:class:`datetime.timezone`.

Modules/_datetimemodule.c

@@ -3741,11 +3741,8 @@ timezone_richcompare(PyDateTime_TimeZone *self,
 {
     if (op != Py_EQ && op != Py_NE)
         Py_RETURN_NOTIMPLEMENTED;
-    if (Py_TYPE(other) != &PyDateTime_TimeZoneType) {
-        if (op == Py_EQ)
-            Py_RETURN_FALSE;
-        else
-            Py_RETURN_TRUE;
+    if (!PyTZInfo_Check(other)) {
+        Py_RETURN_NOTIMPLEMENTED;
     }
     return delta_richcompare(self->offset, other->offset, op);
 }