BUG: (pandas 3.0rc0) `.str.isdigit` regression for fractional powers

[galipremsagar]

Pandas version checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

In [1]: import pandas as pd

In [2]: pd.__version__
Out[2]: '3.0.0rc0'

In [3]: s = pd.Series(["23", "³", "⅕", ""])

In [4]: s.str.isdigit()
Out[4]: 
0     True
1     True
2     True
3    False
dtype: bool

Issue Description

If there is a fractional power, pandas .str.isdigit used to return True, in 3.0rc0, it returns False

Expected Behavior

In [4]: s.str.isdigit()
Out[4]: 
0     True
1     True
2    False
3    False
dtype: bool

Installed Versions

Details

In [5]: pd.show_versions()

INSTALLED VERSIONS

commit : 1a3230d
python : 3.13.11
python-bits : 64
OS : Linux
OS-release : 6.14.0-36-generic
Version : #36~24.04.1-Ubuntu SMP PREEMPT_DYNAMIC Wed Oct 15 15:45:17 UTC 2
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 3.0.0rc0
numpy : 2.2.6
dateutil : 2.9.0.post0
pip : 25.3
Cython : 3.1.7
sphinx : 8.2.3
IPython : 9.8.0
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.14.3
bottleneck : None
fastparquet : None
fsspec : 2025.12.0
html5lib : None
hypothesis : 6.148.7
gcsfs : None
jinja2 : 3.1.6
lxml.etree : None
matplotlib : None
numba : 0.61.2
numexpr : None
odfpy : None
openpyxl : 3.1.5
psycopg2 : None
pymysql : None
pyarrow : 21.0.0
pyiceberg : None
pyreadstat : None
pytest : 9.0.2
python-calamine : None
pytz : 2025.2
pyxlsb : None
s3fs : 2025.12.0
scipy : 1.16.3
sqlalchemy : 2.0.45
tables : None
tabulate : 0.9.0
xarray : None
xlrd : None
xlsxwriter : None
zstandard : 0.25.0
qtpy : None
pyqt5 : None

[rhshadrach]

Thanks for the report; discuss here: #61466 (comment)

As a result of that discussion, we've updated the docs on this function.

https://pandas.pydata.org/docs/dev/reference/api/pandas.Series.str.isdigit.html

The exact behavior of this method, i.e. which unicode characters are considered as digits, depends on the backend used for string operations, and there can be small differences. For example, Python considers the ³ superscript character as a digit, but not the ⅕ fraction character, while PyArrow considers both as digits. For simple (ascii) decimal numbers, the behaviour is consistent.