Backport PR #55051 on branch 2.1.x (Fix pickle roundtrip for new arro…

…w string dtype) (#55054)

Backport PR #55051: Fix pickle roundtrip for new arrow string dtype

Co-authored-by: Patrick Hoefler <61934744+phofl@users.noreply.github.com>

pandas/core/arrays/string_arrow.py

@@ -466,7 +466,10 @@ def _result_converter(cls, values, na=None):
     def __getattribute__(self, item):
         # ArrowStringArray and we both inherit from ArrowExtensionArray, which
         # creates inheritance problems (Diamond inheritance)
-        if item in ArrowStringArrayMixin.__dict__ and item != "_pa_array":
+        if item in ArrowStringArrayMixin.__dict__ and item not in (
+            "_pa_array",
+            "__dict__",
+        ):
             return partial(getattr(ArrowStringArrayMixin, item), self)
         return super().__getattribute__(item)
 

pandas/tests/arrays/string_/test_string_arrow.py

@@ -241,9 +241,10 @@ def test_setitem_invalid_indexer_raises():
 
 
 @skip_if_no_pyarrow
-def test_pickle_roundtrip():
+@pytest.mark.parametrize("dtype", ["string[pyarrow]", "string[pyarrow_numpy]"])
+def test_pickle_roundtrip(dtype):
     # GH 42600
-    expected = pd.Series(range(10), dtype="string[pyarrow]")
+    expected = pd.Series(range(10), dtype=dtype)
     expected_sliced = expected.head(2)
     full_pickled = pickle.dumps(expected)
     sliced_pickled = pickle.dumps(expected_sliced)