ENH: match stdlib behavior for datetimelike comparisons

doc/source/whatsnew/v1.2.0.rst

@@ -307,6 +307,7 @@ Datetimelike
 - Bug in :meth:`DatetimeIndex.searchsorted`, :meth:`TimedeltaIndex.searchsorted`, :meth:`PeriodIndex.searchsorted`, and :meth:`Series.searchsorted` with ``datetime64``, ``timedelta64`` or ``Period`` dtype placement of ``NaT`` values being inconsistent with ``NumPy`` (:issue:`36176`, :issue:`36254`)
 - Inconsistency in :class:`DatetimeArray`, :class:`TimedeltaArray`, and :class:`PeriodArray`  setitem casting arrays of strings to datetimelike scalars but not scalar strings (:issue:`36261`)
 - Bug in :class:`DatetimeIndex.shift` incorrectly raising when shifting empty indexes (:issue:`14811`)
+- :class:`Timestamp` and :class:`DatetimeIndex` comparisons between timezone-aware and timezone-naive objects now follow the standard library ``datetime`` behavior, returning ``True``/``False`` for ``!=``/``==`` and raising for inequality comparisons (:issue:`28507`)
 - Bug in :meth:`DatetimeIndex.equals` and :meth:`TimedeltaIndex.equals` incorrectly considering ``int64`` indexes as equal (:issue:`36744`)
 
 Timedelta

pandas/_libs/lib.pyx

@@ -584,13 +584,6 @@ def array_equivalent_object(left: object[:], right: object[:]) -> bool:
             elif not (PyObject_RichCompareBool(x, y, Py_EQ) or
                       (x is None or is_nan(x)) and (y is None or is_nan(y))):
                 return False
-        except TypeError as err:
-            # Avoid raising TypeError on tzawareness mismatch
-            # TODO: This try/except can be removed if/when Timestamp
-            #  comparisons are changed to match datetime, see GH#28507
-            if "tz-naive and tz-aware" in str(err):
-                return False
-            raise
         except ValueError:
             # Avoid raising ValueError when comparing Numpy arrays to other types
             if cnp.PyArray_IsAnyScalar(x) != cnp.PyArray_IsAnyScalar(y):

pandas/_libs/tslibs/timestamps.pxd

@@ -19,8 +19,8 @@ cdef class _Timestamp(ABCTimestamp):
     cdef bint _get_start_end_field(self, str field)
     cdef _get_date_name_field(self, str field, object locale)
     cdef int64_t _maybe_convert_value_to_local(self)
+    cdef bint _can_compare(self, datetime other)
     cpdef to_datetime64(self)
-    cdef _assert_tzawareness_compat(_Timestamp self, datetime other)
     cpdef datetime to_pydatetime(_Timestamp self, bint warn=*)
     cdef bint _compare_outside_nanorange(_Timestamp self, datetime other,
                                          int op) except -1

pandas/_libs/tslibs/timestamps.pyx

@@ -260,6 +260,10 @@ cdef class _Timestamp(ABCTimestamp):
             if other.dtype.kind == "M":
                 if self.tz is None:
                     return PyObject_RichCompare(self.asm8, other, op)
+                elif op == Py_NE:
+                    return np.ones(other.shape, dtype=np.bool_)
+                elif op == Py_EQ:
+                    return np.zeros(other.shape, dtype=np.bool_)
                 raise TypeError(
                     "Cannot compare tz-naive and tz-aware timestamps"
                 )
@@ -278,24 +282,28 @@ cdef class _Timestamp(ABCTimestamp):
         else:
             return NotImplemented
 
-        self._assert_tzawareness_compat(ots)
+        if not self._can_compare(ots):
+            if op == Py_NE or op == Py_EQ:
+                return NotImplemented
+            raise TypeError(
+                "Cannot compare tz-naive and tz-aware timestamps"
+            )
         return cmp_scalar(self.value, ots.value, op)
 
     cdef bint _compare_outside_nanorange(_Timestamp self, datetime other,
                                          int op) except -1:
         cdef:
             datetime dtval = self.to_pydatetime()
 
-        self._assert_tzawareness_compat(other)
+        if not self._can_compare(other):
+            return NotImplemented
+
         return PyObject_RichCompareBool(dtval, other, op)
 
-    cdef _assert_tzawareness_compat(_Timestamp self, datetime other):
-        if self.tzinfo is None:
-            if other.tzinfo is not None:
-                raise TypeError('Cannot compare tz-naive and tz-aware '
-                                'timestamps')
-        elif other.tzinfo is None:
-            raise TypeError('Cannot compare tz-naive and tz-aware timestamps')
+    cdef bint _can_compare(self, datetime other):
+        if self.tzinfo is not None:
+            return other.tzinfo is not None
+        return other.tzinfo is None
 
     def __add__(self, other):
         cdef:

pandas/core/arrays/datetimelike.py

@@ -685,7 +685,11 @@ def _validate_comparison_value(self, other, opname: str):
 
         if isinstance(other, self._recognized_scalars) or other is NaT:
             other = self._scalar_type(other)  # type: ignore[call-arg]
-            self._check_compatible_with(other)
+            try:
+                self._check_compatible_with(other)
+            except TypeError as err:
+                # e.g. tzawareness mismatch
+                raise InvalidComparison(other) from err
 
         elif not is_list_like(other):
             raise InvalidComparison(other)
@@ -696,8 +700,13 @@ def _validate_comparison_value(self, other, opname: str):
         else:
             try:
                 other = self._validate_listlike(other, opname, allow_object=True)
+                self._check_compatible_with(other)
             except TypeError as err:
-                raise InvalidComparison(other) from err
+                if is_object_dtype(getattr(other, "dtype", None)):
+                    # We will have to operate element-wise
+                    pass
+                else:
+                    raise InvalidComparison(other) from err
 
         return other
 

pandas/tests/arithmetic/test_datetime64.py

@@ -549,26 +549,30 @@ def test_comparison_tzawareness_compat(self, op, box_with_array):
         dr = tm.box_expected(dr, box)
         dz = tm.box_expected(dz, box)
 
-        msg = "Cannot compare tz-naive and tz-aware"
-        with pytest.raises(TypeError, match=msg):
-            op(dr, dz)
-
         if box is pd.DataFrame:
             tolist = lambda x: x.astype(object).values.tolist()[0]
         else:
             tolist = list
 
-        with pytest.raises(TypeError, match=msg):
-            op(dr, tolist(dz))
-        with pytest.raises(TypeError, match=msg):
-            op(dr, np.array(tolist(dz), dtype=object))
-        with pytest.raises(TypeError, match=msg):
-            op(dz, dr)
+        if op not in [operator.eq, operator.ne]:
+            msg = (
+                r"Invalid comparison between dtype=datetime64\[ns.*\] "
+                "and (Timestamp|DatetimeArray|list|ndarray)"
+            )
+            with pytest.raises(TypeError, match=msg):
+                op(dr, dz)
 
-        with pytest.raises(TypeError, match=msg):
-            op(dz, tolist(dr))
-        with pytest.raises(TypeError, match=msg):
-            op(dz, np.array(tolist(dr), dtype=object))
+            with pytest.raises(TypeError, match=msg):
+                op(dr, tolist(dz))
+            with pytest.raises(TypeError, match=msg):
+                op(dr, np.array(tolist(dz), dtype=object))
+            with pytest.raises(TypeError, match=msg):
+                op(dz, dr)
+
+            with pytest.raises(TypeError, match=msg):
+                op(dz, tolist(dr))
+            with pytest.raises(TypeError, match=msg):
+                op(dz, np.array(tolist(dr), dtype=object))
 
         # The aware==aware and naive==naive comparisons should *not* raise
         assert np.all(dr == dr)
@@ -600,17 +604,20 @@ def test_comparison_tzawareness_compat_scalars(self, op, box_with_array):
         ts_tz = pd.Timestamp("2000-03-14 01:59", tz="Europe/Amsterdam")
 
         assert np.all(dr > ts)
-        msg = "Cannot compare tz-naive and tz-aware"
-        with pytest.raises(TypeError, match=msg):
-            op(dr, ts_tz)
+        msg = r"Invalid comparison between dtype=datetime64\[ns.*\] and Timestamp"
+        if op not in [operator.eq, operator.ne]:
+            with pytest.raises(TypeError, match=msg):
+                op(dr, ts_tz)
 
         assert np.all(dz > ts_tz)
-        with pytest.raises(TypeError, match=msg):
-            op(dz, ts)
+        if op not in [operator.eq, operator.ne]:
+            with pytest.raises(TypeError, match=msg):
+                op(dz, ts)
 
-        # GH#12601: Check comparison against Timestamps and DatetimeIndex
-        with pytest.raises(TypeError, match=msg):
-            op(ts, dz)
+        if op not in [operator.eq, operator.ne]:
+            # GH#12601: Check comparison against Timestamps and DatetimeIndex
+            with pytest.raises(TypeError, match=msg):
+                op(ts, dz)
 
     @pytest.mark.parametrize(
         "op",
@@ -628,15 +635,31 @@ def test_comparison_tzawareness_compat_scalars(self, op, box_with_array):
     def test_scalar_comparison_tzawareness(
         self, op, other, tz_aware_fixture, box_with_array
     ):
+        box = box_with_array
         tz = tz_aware_fixture
         dti = pd.date_range("2016-01-01", periods=2, tz=tz)
+        xbox = box if box not in [pd.Index, pd.array] else np.ndarray
 
         dtarr = tm.box_expected(dti, box_with_array)
-        msg = "Cannot compare tz-naive and tz-aware"
-        with pytest.raises(TypeError, match=msg):
-            op(dtarr, other)
-        with pytest.raises(TypeError, match=msg):
-            op(other, dtarr)
+        if op in [operator.eq, operator.ne]:
+            exbool = op is operator.ne
+            expected = np.array([exbool, exbool], dtype=bool)
+            expected = tm.box_expected(expected, xbox)
+
+            result = op(dtarr, other)
+            tm.assert_equal(result, expected)
+
+            result = op(other, dtarr)
+            tm.assert_equal(result, expected)
+        else:
+            msg = (
+                r"Invalid comparison between dtype=datetime64\[ns, .*\] "
+                f"and {type(other).__name__}"
+            )
+            with pytest.raises(TypeError, match=msg):
+                op(dtarr, other)
+            with pytest.raises(TypeError, match=msg):
+                op(other, dtarr)
 
     @pytest.mark.parametrize(
         "op",
@@ -736,10 +759,8 @@ def test_dti_cmp_object_dtype(self):
         tm.assert_numpy_array_equal(result, expected)
 
         other = dti.tz_localize(None)
-        msg = "Cannot compare tz-naive and tz-aware"
-        with pytest.raises(TypeError, match=msg):
-            # tzawareness failure
-            dti != other
+        result = dti != other
+        tm.assert_numpy_array_equal(result, expected)
 
         other = np.array(list(dti[:5]) + [Timedelta(days=1)] * 5)
         result = dti == other

pandas/tests/reductions/test_reductions.py

@@ -56,13 +56,13 @@ def test_ops(self, opname, obj):
             expected = getattr(obj.values, opname)()
         else:
             expected = pd.Period(ordinal=getattr(obj.asi8, opname)(), freq=obj.freq)
-        try:
-            assert result == expected
-        except TypeError:
-            # comparing tz-aware series with np.array results in
-            # TypeError
+
+        if getattr(obj, "tz", None) is not None:
+            # We need to de-localize before comparing to the numpy-produced result
             expected = expected.astype("M8[ns]").astype("int64")
             assert result.value == expected
+        else:
+            assert result == expected
 
     @pytest.mark.parametrize("opname", ["max", "min"])
     @pytest.mark.parametrize(

pandas/tests/scalar/timestamp/test_comparisons.py

@@ -56,9 +56,18 @@ def test_comparison_dt64_ndarray_tzaware(self, reverse, all_compare_operators):
         if reverse:
             left, right = arr, ts
 
-        msg = "Cannot compare tz-naive and tz-aware timestamps"
-        with pytest.raises(TypeError, match=msg):
-            op(left, right)
+        if op is operator.eq:
+            expected = np.array([False, False], dtype=bool)
+            result = op(left, right)
+            tm.assert_numpy_array_equal(result, expected)
+        elif op is operator.ne:
+            expected = np.array([True, True], dtype=bool)
+            result = op(left, right)
+            tm.assert_numpy_array_equal(result, expected)
+        else:
+            msg = "Cannot compare tz-naive and tz-aware timestamps"
+            with pytest.raises(TypeError, match=msg):
+                op(left, right)
 
     def test_comparison_object_array(self):
         # GH#15183
@@ -139,10 +148,8 @@ def test_cant_compare_tz_naive_w_aware(self, utc_fixture):
         b = Timestamp("3/12/2012", tz=utc_fixture)
 
         msg = "Cannot compare tz-naive and tz-aware timestamps"
-        with pytest.raises(TypeError, match=msg):
-            a == b
-        with pytest.raises(TypeError, match=msg):
-            a != b
+        assert not a == b
+        assert a != b
         with pytest.raises(TypeError, match=msg):
             a < b
         with pytest.raises(TypeError, match=msg):
@@ -152,10 +159,8 @@ def test_cant_compare_tz_naive_w_aware(self, utc_fixture):
         with pytest.raises(TypeError, match=msg):
             a >= b
 
-        with pytest.raises(TypeError, match=msg):
-            b == a
-        with pytest.raises(TypeError, match=msg):
-            b != a
+        assert not b == a
+        assert b != a
         with pytest.raises(TypeError, match=msg):
             b < a
         with pytest.raises(TypeError, match=msg):

pandas/tests/series/indexing/test_datetime.py

@@ -258,7 +258,7 @@ def test_getitem_setitem_datetimeindex():
 
     lb = datetime(1990, 1, 1, 4)
     rb = datetime(1990, 1, 1, 7)
-    msg = "Cannot compare tz-naive and tz-aware datetime-like objects"
+    msg = r"Invalid comparison between dtype=datetime64\[ns, US/Eastern\] and datetime"
     with pytest.raises(TypeError, match=msg):
         # tznaive vs tzaware comparison is invalid
         # see GH#18376, GH#18162