BUG: Bug in .loc partial setting with a np.datetime64 (GH9516)

doc/source/whatsnew/v0.16.0.txt

@@ -227,7 +227,7 @@ Bug Fixes
   column with timezone info) to the according sqlalchemy type (:issue:`9085`).
 - Fixed bug in ``to_sql`` ``dtype`` argument not accepting an instantiated
   SQLAlchemy type  (:issue:`9083`).
-
+- Bug in ``.loc`` partial setting with a ``np.datetime64`` (:issue:`9516`)
 
 - Items in ``Categorical.unique()`` (and ``s.unique()`` if ``s`` is of dtype ``category``) now appear in the order in which they are originally found, not in sorted order (:issue:`9331`). This is now consistent with the behavior for other dtypes in pandas.
 

pandas/core/indexing.py

@@ -246,6 +246,7 @@ def _setitem_with_indexer(self, indexer, value):
                         new_indexer = convert_from_missing_indexer_tuple(
                             indexer, self.obj.axes)
                         self._setitem_with_indexer(new_indexer, value)
+
                         return self.obj
 
                     # reindex the axis

pandas/tests/test_indexing.py

@@ -3171,6 +3171,22 @@ def test_partial_setting_with_datetimelike_dtype(self):
         df.loc[mask, 'C'] = df.loc[mask].index
         assert_frame_equal(df, expected)
 
+    def test_loc_setitem_datetime(self):
+
+        # GH 9516
+        dt1 = Timestamp('20130101 09:00:00')
+        dt2 = Timestamp('20130101 10:00:00')
+
+        for conv in [lambda x: x, lambda x: x.to_datetime64(),
+                     lambda x: x.to_pydatetime(), lambda x: np.datetime64(x)]:
+
+            df = pd.DataFrame()
+            df.loc[conv(dt1),'one'] = 100
+            df.loc[conv(dt2),'one'] = 200
+
+            expected = DataFrame({'one' : [100.0,200.0]},index=[dt1,dt2])
+            assert_frame_equal(df, expected)
+
     def test_series_partial_set(self):
         # partial set with new index
         # Regression from GH4825

pandas/tseries/index.py

@@ -1509,7 +1509,7 @@ def insert(self, loc, item):
         """
 
         freq = None
-        if isinstance(item, datetime):
+        if isinstance(item, (datetime, np.datetime64)):
             zone = tslib.get_timezone(self.tz)
             izone = tslib.get_timezone(getattr(item, 'tzinfo', None))
             if zone != izone: