Pandas version checks
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[x] I have checked that this issue has not already been reported.
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[x] I have confirmed this bug exists on the latest version of pandas.
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[x] I have confirmed this bug exists on the main branch of pandas.
Reproducible Example
import pandas as pd
ind = pd.date_range("1/1/2021", "1/5/2021") - pd.Timestamp("1/3/2019")
ind.shift(1)
Issue Description
This only occurs on main. NOT a current bug in pandas.
Gives error:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "C:\Code\pandas_dev\pandas\pandas\core\indexes\datetimelike.py", line 512, in shift
raise NullFrequencyError("Cannot shift with no freq")
pandas.errors.NullFrequencyError: Cannot shift with no freq
The above code works fine with pandas 2.3.
Expected Behavior
No error. A user doing a calculation that produces a TimedeltaIndex can't be expected to set the freq of the index.
I think was introduced by @jbrockmendel in #61985
Installed Versions
INSTALLED VERSIONS
------------------
commit : bb10b27dea9d9a2476de4c8122e0346689e1c9c3
python : 3.11.13
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.26100
machine : AMD64
processor : Intel64 Family 6 Model 183 Stepping 1, GenuineIntel
byteorder : little
LC_ALL : None
LANG : None
LOCALE : English_United States.1252
pandas : 3.0.0.dev0+2306.gbb10b27dea.dirty
numpy : 2.2.6
dateutil : 2.9.0.post0
pip : 25.2
Cython : 3.1.2
sphinx : 8.2.3
IPython : 9.4.0
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.13.4
bottleneck : 1.5.0
fastparquet : 2024.11.0
fsspec : 2025.7.0
html5lib : 1.1
hypothesis : 6.137.3
gcsfs : 2025.7.0
jinja2 : 3.1.6
lxml.etree : 6.0.0
matplotlib : 3.10.5
numba : 0.61.2
numexpr : 2.10.2
odfpy : None
openpyxl : 3.1.5
psycopg2 : 2.9.10
pymysql : 1.4.6
pyarrow : 19.0.1
pyiceberg : 0.9.1
pyreadstat : 1.3.0
pytest : 8.4.1
python-calamine : None
pytz : 2025.2
pyxlsb : 1.0.10
s3fs : 2025.7.0
scipy : 1.16.1
sqlalchemy : 2.0.43
tables : 3.10.2
tabulate : 0.9.0
xarray : 2025.7.1
xlrd : 2.0.1
xlsxwriter : 3.2.5
zstandard : 0.23.0
qtpy : None
pyqt5 : None
Comment From: jbrockmendel
Should be straightforward to add this case to _get_arithmetic_result_freq. Marking as Good First Issue.