REGR: Index.astype(<numpy string dtype>) started failing #50127
Description
On pandas 1.5:
In [2]: pd.Index(['a', 'b']).astype("S3") Out[2]: Index([b'a', b'b'], dtype='object') On the main branch:
In [2]: pd.Index(['a', 'b']).astype("S3") ... File ~/scipy/pandas/pandas/core/indexes/base.py:589, in Index._dtype_to_subclass(cls, dtype) 584 elif issubclass( 585 dtype.type, (str, bool, np.bool_, complex, np.complex64, np.complex128) 586 ): 587 return Index --> 589 raise NotImplementedError(dtype) NotImplementedError: |S3 This started to fail a while ago on pyarrow's CI (https://issues.apache.org/jira/browse/ARROW-18394). This comes up if you roundtrip a pandas DataFrame with bytes column names to arrow and back to pandas.
Didn't yet investigate further what might be the change that caused this / whether this was intentional, etc.