BUG: core/generic/_update_inplace not resetting item_cache (GH5628)

Author: jreback

doc/source/release.rst

@@ -209,7 +209,7 @@ Improvements to existing features
   - ``NDFrame.drop()``, ``NDFrame.dropna()``, and ``.drop_duplicates()`` all
     accept ``inplace`` as a kewyord argument; however, this only means that the
     wrapper is updated inplace, a copy is still made internally.
-    (:issue:`1960`, :issue:`5247`, and related :issue:`2325` [still not
+    (:issue:`1960`, :issue:`5247`, :issue:`5628`, and related :issue:`2325` [still not
     closed])
   - Fixed bug in `tools.plotting.andrews_curvres` so that lines are drawn grouped
     by color as expected.

pandas/core/generic.py

@@ -1217,6 +1217,7 @@ def _update_inplace(self, result):
         # NOTE: This does *not* call __finalize__ and that's an explicit
         # decision that we may revisit in the future.
         self._reset_cache()
+        self._clear_item_cache()
         self._data = result._data
         self._maybe_update_cacher()
 

pandas/tests/test_frame.py

@@ -6806,6 +6806,13 @@ def test_drop(self):
         assert_frame_equal(nu_df.drop('X', axis='rows'), nu_df.ix[["Y"], :])
         assert_frame_equal(nu_df.drop(['X', 'Y'], axis=0), nu_df.ix[[], :])
 
+        # inplace cache issue
+        # GH 5628
+        df = pd.DataFrame(np.random.randn(10,3), columns=list('abc'))
+        expected = df[~(df.b>0)]
+        df.drop(labels=df[df.b>0].index, inplace=True)
+        assert_frame_equal(df,expected)
+
     def test_fillna(self):
         self.tsframe['A'][:5] = nan
         self.tsframe['A'][-5:] = nan