BUG: np.str_ not supported in df.loc

[auderson]

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Reproducible Example

df = pd.DataFrame(index=pd.date_range('2021', '2022'))
df.loc[np.array(['2021/6/1'])[0]:]

Issue Description

The above code throws the following error:

Traceback (most recent call last):
  File "/home/auderson/miniconda3/lib/python3.8/site-packages/IPython/core/interactiveshell.py", line 3444, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-8-71a904a69823>", line 1, in <module>
    df.loc[np.array(['2021/6/1'])[0]:]
  File "/home/auderson/miniconda3/lib/python3.8/site-packages/pandas/core/indexing.py", line 966, in __getitem__
    return self._getitem_axis(maybe_callable, axis=axis)
  File "/home/auderson/miniconda3/lib/python3.8/site-packages/pandas/core/indexing.py", line 1179, in _getitem_axis
    return self._get_slice_axis(key, axis=axis)
  File "/home/auderson/miniconda3/lib/python3.8/site-packages/pandas/core/indexing.py", line 1213, in _get_slice_axis
    indexer = labels.slice_indexer(slice_obj.start, slice_obj.stop, slice_obj.step)
  File "/home/auderson/miniconda3/lib/python3.8/site-packages/pandas/core/indexes/datetimes.py", line 743, in slice_indexer
    return Index.slice_indexer(self, start, end, step, kind=kind)
  File "/home/auderson/miniconda3/lib/python3.8/site-packages/pandas/core/indexes/base.py", line 6246, in slice_indexer
    start_slice, end_slice = self.slice_locs(start, end, step=step)
  File "/home/auderson/miniconda3/lib/python3.8/site-packages/pandas/core/indexes/base.py", line 6456, in slice_locs
    start_slice = self.get_slice_bound(start, "left")
  File "/home/auderson/miniconda3/lib/python3.8/site-packages/pandas/core/indexes/datetimes.py", line 778, in get_slice_bound
    return super().get_slice_bound(label, side=side, kind=kind)
  File "/home/auderson/miniconda3/lib/python3.8/site-packages/pandas/core/indexes/base.py", line 6365, in get_slice_bound
    label = self._maybe_cast_slice_bound(label, side)
  File "/home/auderson/miniconda3/lib/python3.8/site-packages/pandas/core/indexes/datetimes.py", line 694, in _maybe_cast_slice_bound
    label = super()._maybe_cast_slice_bound(label, side, kind=kind)
  File "/home/auderson/miniconda3/lib/python3.8/site-packages/pandas/core/indexes/datetimelike.py", line 310, in _maybe_cast_slice_bound
    parsed, reso = self._parse_with_reso(label)
  File "/home/auderson/miniconda3/lib/python3.8/site-packages/pandas/core/indexes/datetimelike.py", line 231, in _parse_with_reso
    parsed, reso_str = parsing.parse_time_string(label, self.freq)
TypeError: Argument 'arg' has incorrect type (expected str, got numpy.str_)

Expected Behavior

There are cases where I'll slice the dataframe with an element from a numpy str array, which has the dtype of np.str_. Not sure if this should be supported by pandas?

Installed Versions

INSTALLED VERSIONS

commit : d023ba7
python : 3.8.10.final.0
python-bits : 64
OS : Linux
OS-release : 5.8.0-63-generic
Version : #71-Ubuntu SMP Tue Jul 13 15:59:12 UTC 2021
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8
pandas : 1.4.0rc0
numpy : 1.20.3
pytz : 2021.3
dateutil : 2.8.2
pip : 21.2.4
setuptools : 58.0.4
Cython : 0.29.24
pytest : 6.2.5
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : 4.6.2
html5lib : 1.1
pymysql : 1.0.2
psycopg2 : 2.8.6 (dt dec pq3 ext lo64)
jinja2 : 2.11.3
IPython : 7.29.0
pandas_datareader: 0.9.0
bs4 : None
bottleneck : None
fsspec : 2021.10.1
fastparquet : None
gcsfs : None
matplotlib : 3.5.0
numexpr : 2.7.3
odfpy : None
openpyxl : 3.0.7
pandas_gbq : None
pyarrow : 6.0.1
pyxlsb : None
s3fs : None
scipy : 1.7.3
sqlalchemy : 1.4.27
tables : None
tabulate : 0.8.9
xarray : None
xlrd : None
xlwt : None
numba : 0.54.1
zstandard : None

[BrieucRyelandt]

``I have the same issue in a project that use a custom subclass of str to access DataFrame fields.
The fixed that was implemented in #45626 only works for numpy.str_ but they might be many cases of packages that have objects inheriting from string.
Why don't you update the fix using issubclass(arg, str) (even isinstance would work) to handle all these cases at a time?
It would avoid to consider each cases one by one.

edit:
If people are looking for a patch, it can be fixed by adding a call method to the custom class:

class CustomClass(str):
    def __call__(self, _) -> str:
        return super().__str__()