ENH: support addition with pyarrow string dtypes (#51338)

* ENH: support addition with pyarrow string dtypes

* use pc.binary_join_element_wise

* mypy fixup

---------

Co-authored-by: Matthew Roeschke <10647082+mroeschke@users.noreply.github.com>

Author: jbrockmendel

pandas/core/arrays/arrow/array.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 from copy import deepcopy
+import operator
 import re
 from typing import (
     TYPE_CHECKING,
@@ -50,6 +51,7 @@
 )
 from pandas.core.dtypes.missing import isna
 
+from pandas.core import roperator
 from pandas.core.arraylike import OpsMixin
 from pandas.core.arrays.base import ExtensionArray
 import pandas.core.common as com
@@ -458,6 +460,29 @@ def _cmp_method(self, other, op):
         return BooleanArray(values, mask)
 
     def _evaluate_op_method(self, other, op, arrow_funcs):
+        pa_type = self._data.type
+        if (pa.types.is_string(pa_type) or pa.types.is_binary(pa_type)) and op in [
+            operator.add,
+            roperator.radd,
+        ]:
+            length = self._data.length()
+
+            seps: list[str] | list[bytes]
+            if pa.types.is_string(pa_type):
+                seps = [""] * length
+            else:
+                seps = [b""] * length
+
+            if is_scalar(other):
+                other = [other] * length
+            elif isinstance(other, type(self)):
+                other = other._data
+            if op is operator.add:
+                result = pc.binary_join_element_wise(self._data, other, seps)
+            else:
+                result = pc.binary_join_element_wise(other, self._data, seps)
+            return type(self)(result)
+
         pc_func = arrow_funcs[op.__name__]
         if pc_func is NotImplemented:
             raise NotImplementedError(f"{op.__name__} not implemented.")

pandas/tests/arrays/string_/test_string.py

@@ -96,15 +96,7 @@ def test_astype_roundtrip(dtype):
     tm.assert_series_equal(result, ser)
 
 
-def test_add(dtype, request):
-    if dtype.storage == "pyarrow":
-        reason = (
-            "unsupported operand type(s) for +: 'ArrowStringArray' and "
-            "'ArrowStringArray'"
-        )
-        mark = pytest.mark.xfail(raises=NotImplementedError, reason=reason)
-        request.node.add_marker(mark)
-
+def test_add(dtype):
     a = pd.Series(["a", "b", "c", None, None], dtype=dtype)
     b = pd.Series(["x", "y", None, "z", None], dtype=dtype)
 
@@ -140,12 +132,7 @@ def test_add_2d(dtype, request):
         s + b
 
 
-def test_add_sequence(dtype, request):
-    if dtype.storage == "pyarrow":
-        reason = "unsupported operand type(s) for +: 'ArrowStringArray' and 'list'"
-        mark = pytest.mark.xfail(raises=NotImplementedError, reason=reason)
-        request.node.add_marker(mark)
-
+def test_add_sequence(dtype):
     a = pd.array(["a", "b", None, None], dtype=dtype)
     other = ["x", None, "y", None]
 

pandas/tests/extension/test_arrow.py

@@ -1013,6 +1013,10 @@ def _get_scalar_exception(self, opname, pa_dtype):
             exc = NotImplementedError
         elif arrow_temporal_supported:
             exc = None
+        elif opname in ["__add__", "__radd__"] and (
+            pa.types.is_string(pa_dtype) or pa.types.is_binary(pa_dtype)
+        ):
+            exc = None
         elif not (pa.types.is_floating(pa_dtype) or pa.types.is_integer(pa_dtype)):
             exc = pa.ArrowNotImplementedError
         else:
@@ -1187,9 +1191,7 @@ def test_add_series_with_extension_array(self, data, request):
             return
 
         if (pa_version_under8p0 and pa.types.is_duration(pa_dtype)) or (
-            pa.types.is_binary(pa_dtype)
-            or pa.types.is_string(pa_dtype)
-            or pa.types.is_boolean(pa_dtype)
+            pa.types.is_boolean(pa_dtype)
         ):
             request.node.add_marker(
                 pytest.mark.xfail(

pandas/tests/strings/test_api.py

@@ -6,7 +6,6 @@
     MultiIndex,
     Series,
     _testing as tm,
-    get_option,
 )
 from pandas.core.strings.accessor import StringMethods
 
@@ -124,16 +123,8 @@ def test_api_per_method(
             method(*args, **kwargs)
 
 
-def test_api_for_categorical(any_string_method, any_string_dtype, request):
+def test_api_for_categorical(any_string_method, any_string_dtype):
     # https://github.com/pandas-dev/pandas/issues/10661
-
-    if any_string_dtype == "string[pyarrow]" or (
-        any_string_dtype == "string" and get_option("string_storage") == "pyarrow"
-    ):
-        # unsupported operand type(s) for +: 'ArrowStringArray' and 'str'
-        mark = pytest.mark.xfail(raises=NotImplementedError, reason="Not Implemented")
-        request.node.add_marker(mark)
-
     s = Series(list("aabb"), dtype=any_string_dtype)
     s = s + " " + s
     c = s.astype("category")