BUG: Series.loc slicing raises KeyError unexpectedly #62990
Description
Pandas version checks
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Reproducible Example
import pandas as pd print(pd.Series([3, 6, 7, 6], index=[3, 6, 7, 9]).loc[5:], "\n") # works print(pd.Series([3, 6, 7, 6], index=[3, 6, 7, 6]).loc[5:], "\n") # raises errorIssue Description
When an index value is repeated, loc slicing raises a KeyError.
The documentation does not mention this as a condition for raising a KeyError.
Expected Behavior
I think this should return d.Series([6, 7, 6], index=[6, 7, 6]) and not raise an error.
Installed Versions
Details
INSTALLED VERSIONS ------------------ commit : 9c8bc3e55188c8aff37207a74f1dd144980b8874 python : 3.10.11 python-bits : 64 OS : Windows OS-release : 10 Version : 10.0.26100 machine : AMD64 processor : Intel64 Family 6 Model 186 Stepping 3, GenuineIntel byteorder : little LC_ALL : None LANG : en_US.UTF-8 LOCALE : English_New Zealand.1252 pandas : 2.3.3 numpy : 2.2.6 pytz : 2025.2 dateutil : 2.9.0.post0 pip : 23.0.1 Cython : None sphinx : None IPython : None adbc-driver-postgresql: None adbc-driver-sqlite : None bs4 : None blosc : None bottleneck : None dataframe-api-compat : None fastparquet : None fsspec : None html5lib : None hypothesis : None gcsfs : None jinja2 : None lxml.etree : None matplotlib : None numba : None numexpr : None odfpy : None openpyxl : None pandas_gbq : None psycopg2 : None pymysql : None pyarrow : None pyreadstat : None pytest : None python-calamine : None pyxlsb : None s3fs : None scipy : None sqlalchemy : None tables : None tabulate : None xarray : None xlrd : None xlsxwriter : None zstandard : None tzdata : 2025.2 qtpy : None pyqt5 : None None