BUG: pandas.tseries.frequencies.to_offset() raises ValueError when parsing a LastWeekOfMonth frequency string

[ypsah]

Pandas version checks

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

• 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.tseries.frequencies.to_offset(pd.offsets.LastWeekOfMonth().freqstr)

Issue Description

The code above raises the following exception:

Traceback (most recent call last):
  File "offsets.pyx", line 4776, in pandas._libs.tslibs.offsets._get_offset
KeyError: 'LWOM'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "offsets.pyx", line 4946, in pandas._libs.tslibs.offsets.to_offset
  File "offsets.pyx", line 4782, in pandas._libs.tslibs.offsets._get_offset
ValueError: Invalid frequency: LWOM-MON, failed to parse with error message: KeyError('LWOM')

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "offsets.pyx", line 4791, in pandas._libs.tslibs.offsets.to_offset
  File "offsets.pyx", line 4954, in pandas._libs.tslibs.offsets.to_offset
ValueError: Invalid frequency: LWOM-MON, failed to parse with error message: ValueError("Invalid frequency: LWOM-MON, failed to parse with error message: KeyError('LWOM')")

I've tracked down the issue to LastWeekOfMonth not being present here:

pandas/pandas/_libs/tslibs/offsets.pyx

Line 4647 in d966462

prefix_mapping = {

.

Expected Behavior

pd.tseries.frequencies.to_offset can parse any LastWeekOfMonth frequency string.

Installed Versions

INSTALLED VERSIONS

commit : d9cdd2e
python : 3.12.4.final.0
python-bits : 64
OS : Linux
OS-release : 6.9.7-arch1-1
Version : #1 SMP PREEMPT_DYNAMIC Fri, 28 Jun 2024 04:32:50 +0000
machine : x86_64
processor :
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 2.2.2
numpy : 2.0.0
pytz : 2024.1
dateutil : 2.9.0.post0
setuptools : None
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
None

[aram-cinnamon]

take

[ypsah]

Thanks