FIX pandas-dev#57645: Cannot use numpy FLS as indicies since pandas 2.2.1

While using the function set_index with parameter inplace=True, the function would try and create a new index where its dtype would be a FLS S{value} dtype, which was not recognized by the function _dtype_to_subclass and raised a NotImplementedError. That said , by adding a verification that recognizes FLS dtype , the index is created successfully and the function executes properly.

Author: PF2100

doc/source/whatsnew/v3.0.0.rst

@@ -308,6 +308,7 @@ Bug fixes
 - Fixed bug in :meth:`Series.diff` allowing non-integer values for the ``periods`` argument. (:issue:`56607`)
 - Fixed bug in :meth:`Series.rank` that doesn't preserve missing values for nullable integers when ``na_option='keep'``. (:issue:`56976`)
 - Fixed bug in :meth:`Series.replace` and :meth:`DataFrame.replace` inconsistently replacing matching instances when ``regex=True`` and missing values are present. (:issue:`56599`)
+- Fixed bug in :class:`Index` Index constructor did not allow FLS as indicies. (:issue:`57645`) 
 
 Categorical
 ^^^^^^^^^^^

pandas/core/indexes/base.py

@@ -626,7 +626,9 @@ def _dtype_to_subclass(cls, dtype: DtypeObj):
             # NB: assuming away MultiIndex
             return Index
 
-        elif issubclass(dtype.type, str) or is_numeric_dtype(dtype):
+        elif (
+            dtype.kind == "S" or issubclass(dtype.type, str) or is_numeric_dtype(dtype)
+        ):
             return Index
 
         raise NotImplementedError(dtype)

pandas/tests/frame/methods/test_set_index.py

@@ -617,6 +617,20 @@ def test_set_index_raise_on_len(
         with pytest.raises(ValueError, match=msg):
             df.set_index(["A", df.A, box(values)], drop=drop, append=append)
 
+    def test_set_index_with_FLS_Dtype(self):
+        string_length = 6
+        in_dtype, df_name = f"S{string_length}", "fruit"
+        data = ["apple", "banana", "orange", "grape"]
+
+        # Create array with FLS(|S{value}) dtype
+        arr = np.array(data, dtype=in_dtype)
+        df = DataFrame(Series(arr), columns=[df_name])
+
+        # This will create a new Index with FLS dtype
+        expected = Index(data=Series(arr), name=df_name)
+        df.set_index(df_name, inplace=True)
+        tm.assert_index_equal(df.index, expected)
+
 
 class TestSetIndexCustomLabelType:
     def test_set_index_custom_label_type(self):

pandas/tests/io/test_parquet.py

@@ -1023,9 +1023,7 @@ def test_columns_dtypes_not_invalid(self, pa):
 
         # bytes
         df.columns = [b"foo", b"bar"]
-        with pytest.raises(NotImplementedError, match="|S3"):
-            # Bytes fails on read_parquet
-            check_round_trip(df, pa)
+        check_round_trip(df, pa)
 
         # python object
         df.columns = [