BUG: Timestamp == date match stdlib

doc/source/whatsnew/v1.2.0.rst

@@ -196,6 +196,7 @@ Deprecations
 - Deprecated parameter ``inplace`` in :meth:`MultiIndex.set_codes` and :meth:`MultiIndex.set_levels` (:issue:`35626`)
 - Deprecated parameter ``dtype`` in :~meth:`Index.copy` on method all index classes. Use the :meth:`Index.astype` method instead for changing dtype(:issue:`35853`)
 - Date parser functions :func:`~pandas.io.date_converters.parse_date_time`, :func:`~pandas.io.date_converters.parse_date_fields`, :func:`~pandas.io.date_converters.parse_all_fields` and :func:`~pandas.io.date_converters.generic_parser` from ``pandas.io.date_converters`` are deprecated and will be removed in a future version; use :func:`to_datetime` instead (:issue:`35741`)
+- Deprecated comparison of :class:`Timestamp` object with ``datetime.date`` objects.  Instead of e.g. ``ts <= mydate`` use ``ts <= pd.Timestamp(mydate)`` (:issue:`36131`)
 
 .. ---------------------------------------------------------------------------
 

pandas/_libs/tslibs/timestamps.pyx

@@ -15,14 +15,15 @@ from numpy cimport int8_t, int64_t, ndarray, uint8_t
 
 cnp.import_array()
 
-from cpython.datetime cimport (  # alias bc `tzinfo` is a kwarg below
+from cpython.datetime cimport (
+    PyDate_Check,
     PyDateTime_Check,
     PyDateTime_IMPORT,
     PyDelta_Check,
     PyTZInfo_Check,
     datetime,
     time,
-    tzinfo as tzinfo_type,
+    tzinfo as tzinfo_type,  # alias bc `tzinfo` is a kwarg below
 )
 from cpython.object cimport Py_EQ, Py_NE, PyObject_RichCompare, PyObject_RichCompareBool
 
@@ -275,6 +276,18 @@ cdef class _Timestamp(ABCTimestamp):
                 return np.zeros(other.shape, dtype=np.bool_)
             return NotImplemented
 
+        elif PyDate_Check(other):
+            # returning NotImplemented defers to the `date` implementation
+            #  which incorrectly drops tz and normalizes to midnight
+            #  before comparing
+            # We follow the stdlib datetime behavior of never being equal
+            warnings.warn(
+                "Comparison of Timestamp with datetime.date is deprecated in "
+                "order to match the standard library behavior.  "
+                "In a future version these will be considered non-comparable."
+                "Use ts == pd.Timestamp(dt) instead.", FutureWarning
+            )
+            return NotImplemented
         else:
             return NotImplemented
 

pandas/tests/frame/indexing/test_indexing.py

@@ -1931,7 +1931,10 @@ def test_setitem_datetime_coercion(self):
         assert pd.Timestamp("2008-08-08") == df.loc[0, "c"]
         assert pd.Timestamp("2008-08-08") == df.loc[1, "c"]
         df.loc[2, "c"] = date(2005, 5, 5)
-        assert pd.Timestamp("2005-05-05") == df.loc[2, "c"]
+        with tm.assert_produces_warning(FutureWarning):
+            # Comparing Timestamp to date obj is deprecated
+            assert pd.Timestamp("2005-05-05") == df.loc[2, "c"]
+        assert pd.Timestamp("2005-05-05").date() == df.loc[2, "c"]
 
     def test_setitem_datetimelike_with_inference(self):
         # GH 7592

pandas/tests/frame/test_constructors.py

@@ -2628,7 +2628,9 @@ def test_datetime_date_tuple_columns_from_dict(self):
         # GH 10863
         v = date.today()
         tup = v, v
-        result = DataFrame({tup: Series(range(3), index=range(3))}, columns=[tup])
+        with tm.assert_produces_warning(FutureWarning, check_stacklevel=False):
+            # GH#36131 comparison of Timestamp vs date
+            result = DataFrame({tup: Series(range(3), index=range(3))}, columns=[tup])
         expected = DataFrame([0, 1, 2], columns=Index(Series([tup])))
         tm.assert_frame_equal(result, expected)
 

pandas/tests/groupby/test_apply.py

@@ -1065,7 +1065,9 @@ def test_apply_with_date_in_multiindex_does_not_convert_to_timestamp():
     )
 
     grp = df.groupby(["A", "B"])
-    result = grp.apply(lambda x: x.head(1))
+    with tm.assert_produces_warning(FutureWarning, check_stacklevel=False):
+        # GH#36131 comparison of Timestamp vs date inside _make_concat_multiindex
+        result = grp.apply(lambda x: x.head(1))
 
     expected = df.iloc[[0, 2, 3]]
     expected = expected.reset_index()

pandas/tests/scalar/timestamp/test_comparisons.py

@@ -133,6 +133,42 @@ def test_compare_invalid(self):
         assert val != np.float64(1)
         assert val != np.int64(1)
 
+    @pytest.mark.parametrize("tz", [None, "US/Pacific"])
+    def test_compare_date(self, tz):
+        # GH#36131 comparing Timestamp with date object is deprecated
+        ts = Timestamp.now(tz)
+        dt = ts.to_pydatetime().date()
+        # These are incorrectly considered as equal because they
+        #  dispatch to the date comparisons which truncates ts
+
+        for left, right in [(ts, dt), (dt, ts)]:
+            with tm.assert_produces_warning(FutureWarning):
+                assert left == right
+            with tm.assert_produces_warning(FutureWarning):
+                assert not left != right
+            with tm.assert_produces_warning(FutureWarning):
+                assert not left < right
+            with tm.assert_produces_warning(FutureWarning):
+                assert left <= right
+            with tm.assert_produces_warning(FutureWarning):
+                assert not left > right
+            with tm.assert_produces_warning(FutureWarning):
+                assert left >= right
+
+        # Once the deprecation is enforced, the following assertions
+        #  can be enabled:
+        #    assert not left == right
+        #    assert left != right
+        #
+        #    with pytest.raises(TypeError):
+        #        left < right
+        #    with pytest.raises(TypeError):
+        #        left <= right
+        #    with pytest.raises(TypeError):
+        #        left > right
+        #    with pytest.raises(TypeError):
+        #        left >= right
+
     def test_cant_compare_tz_naive_w_aware(self, utc_fixture):
         # see GH#1404
         a = Timestamp("3/12/2012")