BUG: datetime64 - Timestamp incorrectly raising TypeError (#28286)

Author: jbrockmendel

doc/source/whatsnew/v1.0.0.rst

@@ -98,6 +98,8 @@ Datetimelike
 - Bug in :meth:`Series.dt` property lookups when the underlying data is read-only (:issue:`27529`)
 - Bug in ``HDFStore.__getitem__`` incorrectly reading tz attribute created in Python 2 (:issue:`26443`)
 - Bug in :meth:`pandas.core.groupby.SeriesGroupBy.nunique` where ``NaT`` values were interfering with the count of unique values (:issue:`27951`)
+- Bug in :class:`Timestamp` subtraction when subtracting a :class:`Timestamp` from a ``np.datetime64`` object incorrectly raising ``TypeError`` (:issue:`28286`)
+-
 
 
 Timedelta

pandas/_libs/tslibs/c_timestamp.pyx

@@ -312,6 +312,11 @@ cdef class _Timestamp(datetime):
             except (OverflowError, OutOfBoundsDatetime):
                 pass
 
+        elif is_datetime64_object(self):
+            # GH#28286 cython semantics for __rsub__, `other` is actually
+            #  the Timestamp
+            return type(other)(self) - other
+
         # scalar Timestamp/datetime - Timedelta -> yields a Timestamp (with
         # same timezone if specified)
         return datetime.__sub__(self, other)

pandas/tests/scalar/timestamp/test_arithmetic.py

@@ -66,6 +66,20 @@ def test_delta_preserve_nanos(self):
         result = val + timedelta(1)
         assert result.nanosecond == val.nanosecond
 
+    def test_rsub_dtscalars(self, tz_naive_fixture):
+        # In particular, check that datetime64 - Timestamp works GH#28286
+        td = Timedelta(1235345642000)
+        ts = Timestamp.now(tz_naive_fixture)
+        other = ts + td
+
+        assert other - ts == td
+        assert other.to_pydatetime() - ts == td
+        if tz_naive_fixture is None:
+            assert other.to_datetime64() - ts == td
+        else:
+            with pytest.raises(TypeError, match="subtraction must have"):
+                other.to_datetime64() - ts
+
     def test_timestamp_sub_datetime(self):
         dt = datetime(2013, 10, 12)
         ts = Timestamp(datetime(2013, 10, 13))