GH34529

correction and test for issue-pandas-dev#34529

made the formating changes

fixing tests on issue-pandas-dev#34529

add whats new entry on issue-pandas-dev#34539

add whats new entry correction issue-pandas-dev#34539

doc/source/whatsnew/v1.1.0.rst

@@ -1032,6 +1032,7 @@ ExtensionArray
 - Fixed bug where :meth:`StringArray.memory_usage` was not implemented (:issue:`33963`)
 - Fixed bug where :meth:`DataFrameGroupBy` would ignore the ``min_count`` argument for aggregations on nullable boolean dtypes (:issue:`34051`)
 - Fixed bug that `DataFrame(columns=.., dtype='string')` would fail (:issue:`27953`, :issue:`33623`)
+- Fixed regression where :meth:`DataFrame.apply` would raise ``ValueError`` for elements whth ``S`` dtype (:issue:`34529`)
 
 Other
 ^^^^^

pandas/core/dtypes/cast.py

@@ -1608,7 +1608,7 @@ def construct_1d_ndarray_preserving_na(
     """
     subarr = np.array(values, dtype=dtype, copy=copy)
 
-    if dtype is not None and dtype.kind in ("U", "S"):
+    if dtype is not None and dtype.kind == "U":
         # GH-21083
         # We can't just return np.array(subarr, dtype='str') since
         # NumPy will convert the non-string objects into strings

pandas/tests/frame/test_apply.py

@@ -785,6 +785,17 @@ def non_reducing_function(val):
             df.applymap(func)
             assert values == df.a.to_list()
 
+    def test_apply_with_byte_string(self):
+        # GH 34529
+        df = pd.DataFrame(np.array([b"abcd", b"efgh"]), columns=["col"])
+        expected = pd.DataFrame(
+            np.array([b"abcd", b"efgh"]), columns=["col"], dtype=object
+        )
+        # After we make the aply we exect a dataframe just
+        # like the original but with the object datatype
+        result = df.apply(lambda x: x.astype("object"))
+        tm.assert_frame_equal(result, expected)
+
 
 class TestInferOutputShape:
     # the user has supplied an opaque UDF where