Pandas version checks
Reproducible Example
import pandas as pd
df = pd.DataFrame(
{"val": [1, 2, 3]},
index=pd.Index(pd.array([1, 2, 3], dtype="Int64"), name="id"),
)
print(df.index.dtype)
print(df.rename({1: 9}).index.dtype)Issue Description
DataFrame.rename() and Series.rename() do not preserve nullable extension dtypes on index/column labels. In the reproduced cases with nullable integer and floating dtypes, renaming labels silently downcasts the result to the corresponding NumPy dtype.
The root cause appears to be Index._transform_index(), which reconstructs the transformed index from a plain Python list instead of preserving/casting through the original ExtensionArray dtype.
Expected Behavior
rename() should preserve the original index dtype after relabeling.
Installed Versions
Details
INSTALLED VERSIONS
commit : 2a7587f
python : 3.12.12
python-bits : 64
OS : Windows
OS-release : 11
Version : 10.0.26200
machine : AMD64
processor : Intel64 Family 6 Model 183 Stepping 1, GenuineIntel
byteorder : little
LC_ALL : None
LANG : None
LOCALE : English_United States.1252
pandas : 3.1.0.dev0+526.g2a7587fed0.dirty
numpy : 2.4.2
dateutil : 2.9.0.post0
pip : 26.0.1
Cython : 3.2.4
sphinx : None
IPython : 9.10.0
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : None
bottleneck : 1.6.0
fastparquet : None
fsspec : None
html5lib : None
hypothesis : 6.151.6
gcsfs : None
jinja2 : None
lxml.etree : None
matplotlib : 3.10.8
numba : None
numexpr : 2.14.1
odfpy : None
openpyxl : None
psycopg2 : None
pymysql : None
pyarrow : None
pyiceberg : None
pyreadstat : None
pytest : 9.0.2
python-calamine : None
pytz : 2025.2
pyxlsb : None
s3fs : None
scipy : 1.17.0
sqlalchemy : 2.0.46
tables : None
tabulate : 0.9.0
xarray : None
xlrd : None
xlsxwriter : None
zstandard : None
qtpy : None
pyqt5 : None
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
Issue Description
DataFrame.rename()andSeries.rename()do not preserve nullable extension dtypes on index/column labels. In the reproduced cases with nullable integer and floating dtypes, renaming labels silently downcasts the result to the corresponding NumPy dtype.The root cause appears to be
Index._transform_index(), which reconstructs the transformed index from a plain Python list instead of preserving/casting through the originalExtensionArraydtype.Expected Behavior
rename()should preserve the original index dtype after relabeling.Installed Versions
Details
INSTALLED VERSIONS
commit : 2a7587f
python : 3.12.12
python-bits : 64
OS : Windows
OS-release : 11
Version : 10.0.26200
machine : AMD64
processor : Intel64 Family 6 Model 183 Stepping 1, GenuineIntel
byteorder : little
LC_ALL : None
LANG : None
LOCALE : English_United States.1252
pandas : 3.1.0.dev0+526.g2a7587fed0.dirty
numpy : 2.4.2
dateutil : 2.9.0.post0
pip : 26.0.1
Cython : 3.2.4
sphinx : None
IPython : 9.10.0
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : None
bottleneck : 1.6.0
fastparquet : None
fsspec : None
html5lib : None
hypothesis : 6.151.6
gcsfs : None
jinja2 : None
lxml.etree : None
matplotlib : 3.10.8
numba : None
numexpr : 2.14.1
odfpy : None
openpyxl : None
psycopg2 : None
pymysql : None
pyarrow : None
pyiceberg : None
pyreadstat : None
pytest : 9.0.2
python-calamine : None
pytz : 2025.2
pyxlsb : None
s3fs : None
scipy : 1.17.0
sqlalchemy : 2.0.46
tables : None
tabulate : 0.9.0
xarray : None
xlrd : None
xlsxwriter : None
zstandard : None
qtpy : None
pyqt5 : None