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BUG: not able to convert non-zero padded hour to timestamp.

See original GitHub issue

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
pd.to_datetime('2018-08-18 9', format='%Y-%m-%d %H', infer_datetime_format=True)

Issue Description

Not able to convert the non-zero padded Hour and zero padded date to timestamp. ParserError: Unknown string format: 2018-08-18 9

Not having any issue converting: pd.to_datetime('2018-08-18 09', format='%Y-%m-%d %H', infer_datetime_format=True) OUTPUT: Timestamp('2018-08-18 09:00:00')

Expected Behavior

I am expecting Timestamp('2018-08-18 09:00:00') with non-zero padded hour.

Installed Versions

INSTALLED VERSIONS

commit : 4bfe3d07b4858144c219b9346329027024102ab6 python : 3.8.13.final.0 python-bits : 64 OS : Windows OS-release : 10 Version : 10.0.19043 machine : AMD64 processor : Intel64 Family 6 Model 78 Stepping 3, GenuineIntel byteorder : little LC_ALL : None LANG : None LOCALE : English_India.1252

pandas : 1.4.2 numpy : 1.20.3 pytz : 2021.3 dateutil : 2.8.2 pip : 21.2.2 setuptools : 58.0.4 Cython : 0.29.25 pytest : 6.2.5 hypothesis : None sphinx : 4.4.0 blosc : None feather : None xlsxwriter : 3.0.2 lxml.etree : 4.7.1 html5lib : 1.1 pymysql : None psycopg2 : 2.9.1 jinja2 : 2.11.3 IPython : 8.2.0 pandas_datareader: None bs4 : 4.10.0 bottleneck : 1.3.4 brotli : fastparquet : None fsspec : 2022.02.0 gcsfs : None markupsafe : 2.0.1 matplotlib : 3.5.0 numba : 0.54.1 numexpr : 2.8.1 odfpy : None openpyxl : 3.0.9 pandas_gbq : None pyarrow : 7.0.0 pyreadstat : None pyxlsb : None s3fs : None scipy : 1.7.3 snappy : None sqlalchemy : 1.4.27 tables : 3.6.1 tabulate : None xarray : None xlrd : 2.0.1 xlwt : 1.3.0 zstandard : None