Pandas version checks

  • [x] I have checked that this issue has not already been reported.

  • [x] 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

print(pd.tseries.api.guess_datetime_format('2025-06-15T21:25:00.000000Z'))
print(pd.tseries.api.guess_datetime_format('2025-06-15T20:24:00.000000Z'))
print(pd.tseries.api.guess_datetime_format('2025-06-15T20:25:00.000000Z'))

# %Y-%m-%dT%H:%M:%S.%f%z
# %Y-%m-%dT%H:%M:%S.%f%z
# None

Issue Description

I'm receiving a strange None from guess_datetime_format for a very particular string combination. I can change the hours and minutes separately and it works fine, but when I set the time to exactly 20:25 it produces a None result.

Expected Behavior

It should produce the same '%Y-%m-%dT%H:%M:%S.%f%z' format as the other two examples.

Installed Versions

INSTALLED VERSIONS ------------------ commit : 2cc37625532045f4ac55b27176454bbbc9baf213 python : 3.10.12 python-bits : 64 OS : Linux OS-release : 6.15.1-061501-generic Version : #202506041425 SMP PREEMPT_DYNAMIC Wed Jun 4 18:01:32 UTC 2025 machine : x86_64 processor : x86_64 byteorder : little LC_ALL : C.UTF-8 LANG : C.UTF-8 LOCALE : en_US.UTF-8 pandas : 2.3.0 numpy : 1.26.4 pytz : 2025.2 dateutil : 2.9.0.post0 pip : 25.0.1 Cython : 0.29.37 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 : 2024.6.1 html5lib : None hypothesis : None gcsfs : None jinja2 : 3.1.4 lxml.etree : None matplotlib : 3.10.3 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 : 1.11.1 sqlalchemy : None tables : None tabulate : None xarray : None xlrd : None xlsxwriter : None zstandard : None tzdata : 2025.2 qtpy : None pyqt5 : None

Comment From: chilin0525

  • Confirmed on 2.3.0:

```python

import pandas as pd print(pd.tseries.api.guess_datetime_format('2025-06-15T21:25:00.000000Z')) %Y-%m-%dT%H:%M:%S.%f%z print(pd.tseries.api.guess_datetime_format('2025-06-15T20:24:00.000000Z')) %Y-%m-%dT%H:%M:%S.%f%z print(pd.tseries.api.guess_datetime_format('2025-06-15T20:25:00.000000Z')) None * Works on the main branch, further investigation is required:python import pandas as pd print(pd.tseries.api.guess_datetime_format('2025-06-15T21:25:00.000000Z')) %Y-%m-%dT%H:%M:%S.%f%z print(pd.tseries.api.guess_datetime_format('2025-06-15T20:24:00.000000Z')) %Y-%m-%dT%H:%M:%S.%f%z print(pd.tseries.api.guess_datetime_format('2025-06-15T20:25:00.000000Z')) %Y-%m-%dT%H:%M:%S.%f%z ```

Comment From: chilin0525

Look like the issue resolved in https://github.com/pandas-dev/pandas/pull/57471, this issue should be able to be closed.

Comment From: asishm

Thanks for the investigation @chilin0525. Closing.

Comment From: logan-dunbar

That pull request was completed over a year ago, will it make it into the next versioned release?

Comment From: asishm

It is currently slated for release with pandas 3.0 unsure if this will get backported to 2.3.x

cc @mroeschke