[backport 2.3.x] BUG: DataFrame.explode fails with str dtype (#61623) (#61699)

BUG: DataFrame.explode fails with str dtype (#61623)

Co-authored-by: Richard Shadrach <45562402+rhshadrach@users.noreply.github.com>

Author: jorisvandenbossche

doc/source/whatsnew/v2.3.1.rst

@@ -26,7 +26,7 @@ Fixed regressions
 
 Bug fixes
 ~~~~~~~~~
--
+- Fixed bug in :meth:`DataFrame.explode` and :meth:`Series.explode` where methods would fail with ``dtype="str"`` (:issue:`61623`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_231.other:

pandas/core/arrays/arrow/array.py

@@ -1923,7 +1923,9 @@ def _explode(self):
         """
         # child class explode method supports only list types; return
         # default implementation for non list types.
-        if not pa.types.is_list(self.dtype.pyarrow_dtype):
+        if not hasattr(self.dtype, "pyarrow_dtype") or (
+            not pa.types.is_list(self.dtype.pyarrow_dtype)
+        ):
             return super()._explode()
         values = self
         counts = pa.compute.list_value_length(values._pa_array)

pandas/tests/frame/methods/test_explode.py

@@ -301,3 +301,11 @@ def test_multi_columns_nan_empty():
         index=[0, 0, 1, 2, 3, 3],
     )
     tm.assert_frame_equal(result, expected)
+
+
+def test_str_dtype():
+    # https://github.com/pandas-dev/pandas/pull/61623
+    df = pd.DataFrame({"a": ["x", "y"]}, dtype="str")
+    result = df.explode(column="a")
+    assert result is not df
+    tm.assert_frame_equal(result, df)

pandas/tests/series/methods/test_explode.py

@@ -173,3 +173,11 @@ def test_explode_pyarrow_non_list_type(ignore_index):
     result = ser.explode(ignore_index=ignore_index)
     expected = pd.Series([1, 2, 3], dtype="int64[pyarrow]", index=[0, 1, 2])
     tm.assert_series_equal(result, expected)
+
+
+def test_str_dtype():
+    # https://github.com/pandas-dev/pandas/pull/61623
+    ser = pd.Series(["x", "y"], dtype="str")
+    result = ser.explode()
+    assert result is not ser
+    tm.assert_series_equal(result, ser)