Fix casting to StringDtype for ArrowExtensionArray duration and decimal types (rapidsai#21230)

Fixes conversion of ArrowExtensionArray columns (duration and decimal128 types) to pandas StringDtype   
  when using `astype('string[python]')` or `astype('string[pyarrow]')`.

Contributes to rapidsai#18659

Authors:
  - Matthew Murray (https://github.com/Matt711)

Approvers:
  - Matthew Roeschke (https://github.com/mroeschke)

URL: rapidsai#21230

Author: Matt711

python/cudf/cudf/core/column/decimal.py

@@ -30,7 +30,6 @@
 )
 from cudf.core.mixins import BinaryOperand
 from cudf.utils.dtypes import (
-    CUDF_STRING_DTYPE,
     cudf_dtype_to_pa_type,
     get_dtype_of_same_kind,
     get_dtype_of_same_type,
@@ -171,12 +170,12 @@ def as_string_column(self, dtype: DtypeObj) -> StringColumn:
                 )
                 return cast(
                     cudf.core.column.string.StringColumn,
-                    type(self).from_pylibcudf(plc_column),
+                    ColumnBase.create(plc_column, dtype),
                 )
         else:
             return cast(
                 cudf.core.column.StringColumn,
-                cudf.core.column.column_empty(0, dtype=CUDF_STRING_DTYPE),
+                cudf.core.column.column_empty(0, dtype=dtype),
             )
 
     def __pow__(self, other: ColumnBinaryOperand) -> ColumnBase:

python/cudf/cudf/core/column/timedelta.py

@@ -19,6 +19,7 @@
 from cudf.core.column.temporal_base import TemporalBaseColumn
 from cudf.errors import MixedTypeError
 from cudf.utils.dtypes import (
+    CUDF_STRING_DTYPE,
     cudf_dtype_from_pa_type,
     cudf_dtype_to_pa_type,
     find_common_type,
@@ -248,27 +249,29 @@ def as_datetime_column(self, dtype: np.dtype) -> None:  # type: ignore[override]
             f"cannot astype a timedelta from {self.dtype} to {dtype}"
         )
 
-    def strftime(self, format: str) -> StringColumn:
+    def strftime(
+        self, format: str, dtype: DtypeObj = CUDF_STRING_DTYPE
+    ) -> StringColumn:
         if len(self) == 0:
             return super().strftime(format)
-        else:
-            with self.access(mode="read", scope="internal"):
-                return cast(
-                    cudf.core.column.string.StringColumn,
-                    type(self).from_pylibcudf(
-                        plc.strings.convert.convert_durations.from_durations(
-                            self.plc_column, format
-                        )
+        with self.access(mode="read", scope="internal"):
+            return cast(
+                cudf.core.column.string.StringColumn,
+                ColumnBase.create(
+                    plc.strings.convert.convert_durations.from_durations(
+                        self.plc_column, format
                     ),
-                )
+                    dtype,
+                ),
+            )
 
     def as_string_column(self, dtype: DtypeObj) -> StringColumn:
         if cudf.get_option("mode.pandas_compatible"):
             if isinstance(dtype, np.dtype) and dtype.kind == "O":
                 raise MixedTypeError(
                     f"cannot astype a timedelta like from {self.dtype} to {dtype}"
                 )
-        return self.strftime("%D days %H:%M:%S")
+        return self.strftime("%D days %H:%M:%S", dtype=dtype)
 
     def as_timedelta_column(self, dtype: np.dtype) -> TimeDeltaColumn:
         if dtype == self.dtype:

python/cudf/cudf/pandas/scripts/conftest-patch.py

@@ -1473,16 +1473,6 @@ def set_copy_on_write_option():
     "tests/extension/test_arrow.py::TestArrowArray::test_accumulate_series[bool-cummin-True]",
     "tests/extension/test_arrow.py::TestArrowArray::test_accumulate_series[bool-cumprod-False]",
     "tests/extension/test_arrow.py::TestArrowArray::test_accumulate_series[bool-cumprod-True]",
-    "tests/extension/test_arrow.py::TestArrowArray::test_astype_string[decimal128(7, 3)-string[pyarrow]]",
-    "tests/extension/test_arrow.py::TestArrowArray::test_astype_string[decimal128(7, 3)-string[python]]",
-    "tests/extension/test_arrow.py::TestArrowArray::test_astype_string[duration[ms]-string[pyarrow]]",
-    "tests/extension/test_arrow.py::TestArrowArray::test_astype_string[duration[ms]-string[python]]",
-    "tests/extension/test_arrow.py::TestArrowArray::test_astype_string[duration[ns]-string[pyarrow]]",
-    "tests/extension/test_arrow.py::TestArrowArray::test_astype_string[duration[ns]-string[python]]",
-    "tests/extension/test_arrow.py::TestArrowArray::test_astype_string[duration[s]-string[pyarrow]]",
-    "tests/extension/test_arrow.py::TestArrowArray::test_astype_string[duration[s]-string[python]]",
-    "tests/extension/test_arrow.py::TestArrowArray::test_astype_string[duration[us]-string[pyarrow]]",
-    "tests/extension/test_arrow.py::TestArrowArray::test_astype_string[duration[us]-string[python]]",
     "tests/extension/test_arrow.py::TestArrowArray::test_reduce_frame[decimal128(7, 3)-mean-False]",
     "tests/extension/test_arrow.py::TestArrowArray::test_reduce_frame[decimal128(7, 3)-median-True]",
     "tests/extension/test_arrow.py::TestArrowArray::test_reduce_frame[decimal128(7, 3)-prod-False]",