BUG: Partial slicing of unordered datetimeindex inconsistent between providing start and end points · Issue #53983 · pandas-dev/pandas (original) (raw)

Pandas version checks

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

import pandas as pd s = pd.Series([1, 2, 3], index=pd.Series(["2001", "2009", "2002"], dtype="datetime64[ns]")) s.loc["1999":] # KeyError s.loc[:"1999"] # Empty series

Issue Description

#37819 deprecated (and #49607 removed) support for looking up by slice in an unordered datetime index when the slice bounds are not in the index. This made datetime indexes behave more like other indexes when they are unordered.

My reading of those issues suggests that the intended behaviour is that asking for a slice where either (or both) of the start or end points are not in the index should raise a KeyError. However, it is only when the start point is not in the index that a KeyError is raised.

Expected Behavior

I would anticipate that this is symmetric. cc @phofl who introduced the logic for these deprecations.

Installed Versions

INSTALLED VERSIONS

commit : 310b376
python : 3.10.11.final.0
python-bits : 64
OS : Linux
OS-release : 5.19.0-46-generic
Version : #47~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Wed Jun 21 15:35:31 UTC 2
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_GB.UTF-8
LOCALE : en_GB.UTF-8

pandas : 2.1.0.dev0+1009.g310b3765f6
numpy : 1.24.3
pytz : 2023.3
dateutil : 2.8.2
setuptools : 67.7.2
pip : 23.1.2
Cython : 0.29.33
pytest : 7.3.2
hypothesis : 6.79.1
sphinx : 6.2.1
blosc : None
feather : None
xlsxwriter : 3.1.2
lxml.etree : 4.9.2
html5lib : 1.1
pymysql : 1.0.3
psycopg2 : 2.9.3
jinja2 : 3.1.2
IPython : 8.14.0
pandas_datareader: None
bs4 : 4.12.2
bottleneck : 1.3.7
brotli :
fastparquet : 2023.4.0
fsspec : 2023.6.0
gcsfs : 2023.6.0
matplotlib : 3.7.1
numba : 0.57.0
numexpr : 2.8.4
odfpy : None
openpyxl : 3.1.2
pandas_gbq : None
pyarrow : 12.0.0
pyreadstat : 1.2.2
pyxlsb : 1.0.10
s3fs : 2023.6.0
scipy : 1.10.1
snappy :
sqlalchemy : 2.0.16
tables : 3.8.0
tabulate : 0.9.0
xarray : 2023.5.0
xlrd : 2.0.1
zstandard : 0.19.0
tzdata : 2023.3
qtpy : None
pyqt5 : None