BUG: to_datetime behaves differently depending of the format of the string provided · Issue #58859 · pandas-dev/pandas (original) (raw)

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Reproducible Example

Python 3.11.7 | packaged by conda-forge | (main, Dec 23 2023, 14:43:09) [GCC 12.3.0] on linux Type "help", "copyright", "credits" or "license" for more information.

import pandas as pd pd.to_datetime("2016-03-11", dayfirst=True) Timestamp('2016-11-03 00:00:00') pd.to_datetime("20160311", dayfirst=True) Timestamp('2016-03-11 00:00:00')

Issue Description

Dates of the format "YYYYDDMM" are not converted correctly by to_datetime() when dayfirst=True. to_datetime() still reads the date characters as the months

Expected Behavior

Python 3.11.7 | packaged by conda-forge | (main, Dec 23 2023, 14:43:09) [GCC 12.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.

import pandas as pd
pd.to_datetime("2016-03-11", dayfirst=True)
Timestamp('2016-11-03 00:00:00')
pd.to_datetime("20160311", dayfirst=True)
Timestamp('2016-11-03 00:00:00')

Installed Versions

INSTALLED VERSIONS

commit : a671b5a
python : 3.11.7.final.0
python-bits : 64
OS : Linux
OS-release : 3.10.0-1160.114.2.el7.x86_64
Version : #1 SMP Sun Mar 3 08🔞39 EST 2024
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 2.1.4
numpy : 1.26.3
pytz : 2023.3.post1
dateutil : 2.8.2
setuptools : 69.0.3
pip : 23.3.2
Cython : 3.0.7
pytest : 7.4.4
hypothesis : 6.94.0
sphinx : 7.2.6
blosc : None
feather : None
xlsxwriter : 3.1.9
lxml.etree : 5.1.0
html5lib : 1.1
pymysql : None
psycopg2 : None
jinja2 : 3.1.3
IPython : 8.20.0
pandas_datareader : None
bs4 : 4.12.2
bottleneck : 1.3.7
dataframe-api-compat: None
fastparquet : 2023.10.1
fsspec : 2023.12.2
gcsfs : None
matplotlib : 3.8.2
numba : 0.58.1
numexpr : 2.8.8
odfpy : None
openpyxl : 3.1.2
pandas_gbq : None
pyarrow : 16.0.0
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.11.4
sqlalchemy : 2.0.25
tables : 3.9.2
tabulate : 0.9.0
xarray : 2023.7.0
xlrd : 2.0.1
zstandard : 0.19.0
tzdata : 2023.4
qtpy : 2.4.1
pyqt5 : None