BUG: to_dict_of_blocks failing to invalidate item_cache (pandas-dev#35874)

Author: jbrockmendel

pandas/core/internals/managers.py

@@ -896,12 +896,7 @@ def to_dict(self, copy: bool = True):
         Returns
         -------
         values : a dict of dtype -> BlockManager
-
-        Notes
-        -----
-        This consolidates based on str(dtype)
         """
-        self._consolidate_inplace()
 
         bd: Dict[str, List[Block]] = {}
         for b in self.blocks:

pandas/tests/frame/test_block_internals.py

@@ -626,3 +626,21 @@ def test_add_column_with_pandas_array(self):
         assert type(df["c"]._mgr.blocks[0]) == ObjectBlock
         assert type(df2["c"]._mgr.blocks[0]) == ObjectBlock
         tm.assert_frame_equal(df, df2)
+
+
+def test_to_dict_of_blocks_item_cache():
+    # Calling to_dict_of_blocks should not poison item_cache
+    df = pd.DataFrame({"a": [1, 2, 3, 4], "b": ["a", "b", "c", "d"]})
+    df["c"] = pd.arrays.PandasArray(np.array([1, 2, None, 3], dtype=object))
+    mgr = df._mgr
+    assert len(mgr.blocks) == 3  # i.e. not consolidated
+
+    ser = df["b"]  # populations item_cache["b"]
+
+    df._to_dict_of_blocks()
+
+    # Check that the to_dict_of_blocks didnt break link between ser and df
+    ser.values[0] = "foo"
+    assert df.loc[0, "b"] == "foo"
+
+    assert df["b"] is ser