BUG: Timestamp.tz and DatetimeIndex.tz are inconsistent when pytz 2024.2 is installed

[boschmic]

Pandas version checks

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• 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

import pandas as pd
t0 = pd.Timestamp("01-01-2000")
print(repr(t0.tz_localize("CET").tz))
print(repr(pd.DatetimeIndex([t0]).tz_localize("CET").tz))

Issue Description

If pytz = "==2024.2" is installed the example prints

<DstTzInfo 'CET' CET+1:00:00 STD>
<DstTzInfo 'CET' LMT+0:18:00 STD>

Downgrading pytzto 2024.1 resolves this issue.

Expected Behavior

The .tz property should produce the same result regardless if the object is a Timestamp or DatetimeIndex. Hence, I expect this example to print

<DstTzInfo 'CET' CET+1:00:00 STD>
<DstTzInfo 'CET' CET+1:00:00 STD>

Installed Versions

INSTALLED VERSIONS ------------------ commit : d9cdd2e python : 3.11.10.final.0 python-bits : 64 OS : Linux OS-release : 6.8.0-40-generic Version : #40~22.04.3-Ubuntu SMP PREEMPT_DYNAMIC Tue Jul 30 17:30:19 UTC 2 machine : x86_64 processor : x86_64 byteorder : little LC_ALL : None LANG : en_US.UTF-8 LOCALE : en_US.UTF-8

pandas : 2.2.2
numpy : 2.1.1
pytz : 2024.2
dateutil : 2.9.0.post0
setuptools : 69.2.0
pip : 24.0
Cython : None
pytest : None
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : None
IPython : None
pandas_datareader : None
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : None
bottleneck : None
dataframe-api-compat : None
fastparquet : None
fsspec : None
gcsfs : None
matplotlib : None
numba : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : None
pyreadstat : None
python-calamine : None
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
zstandard : None
tzdata : 2024.1
qtpy : None
pyqt5 : None

[lithomas1]

Thanks for reporting this.

I think we spotted this in our CI for pandas 2.2.x as well.

@mroeschke
Sorry to ping but do you know what's going wrong?
Looking at pytz's release it looks like all they did was update their tzdata to IANA 2024b.
Maybe we have a conflict between pytz and zoneinfo/tzdata?

[mroeschke]

Given the documentation in https://pandas.pydata.org/docs/user_guide/timeseries.html#working-with-time-zones (in the Note below), it seems that the ==2024.2 pytz behavior is more correct then the prior.

I don't exactly recall seeing this in the 2.2.x branch.

Additionally, the pandas main branch already removed support for interpreting CET as a pytz timezone and now will infer this as a zoneinfo timezone, so I'm not sure this is likely to be fixed