BUG: TimedeltaArray.astype(duration[{unit}][pyarrow]) (#49795)

* check for np.dtype

* whatsnew

Author: lukemanley

doc/source/whatsnew/v2.0.0.rst

@@ -654,6 +654,8 @@ Conversion
 - Bug where any :class:`ExtensionDtype` subclass with ``kind="M"`` would be interpreted as a timezone type (:issue:`34986`)
 - Bug in :class:`.arrays.ArrowExtensionArray` that would raise ``NotImplementedError`` when passed a sequence of strings or binary (:issue:`49172`)
 - Bug in :func:`to_datetime` was not respecting ``exact`` argument when ``format`` was an ISO8601 format (:issue:`12649`)
+- Bug in :meth:`TimedeltaArray.astype` raising ``TypeError`` when converting to a pyarrow duration type (:issue:`49795`)
+-
 
 Strings
 ^^^^^^^

pandas/core/arrays/timedeltas.py

@@ -332,7 +332,7 @@ def astype(self, dtype, copy: bool = True):
         # DatetimeLikeArrayMixin super call handles other cases
         dtype = pandas_dtype(dtype)
 
-        if dtype.kind == "m":
+        if isinstance(dtype, np.dtype) and dtype.kind == "m":
             if dtype == self.dtype:
                 if copy:
                     return self.copy()

pandas/tests/extension/test_arrow.py

@@ -1369,3 +1369,12 @@ def test_pickle_roundtrip(data):
 
     result_sliced = pickle.loads(sliced_pickled)
     tm.assert_series_equal(result_sliced, expected_sliced)
+
+
+def test_astype_from_non_pyarrow(data):
+    # GH49795
+    pd_array = data._data.to_pandas().array
+    result = pd_array.astype(data.dtype)
+    assert not isinstance(pd_array.dtype, ArrowDtype)
+    assert isinstance(result.dtype, ArrowDtype)
+    tm.assert_extension_array_equal(result, data)