As of polars 1.8.x (but not 1.7.x), partition_by with as_dict=True strips leading zeros from strings on the partition column

[ptomecek]

Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

pl.DataFrame({"s":["01", "0010", "10", "foo"]}).partition_by("s", as_dict=True).keys()

Log output

No response

Issue description

Leading zeros have been stripped from the keys
dict_keys([('1',), ('10',), ('foo',)])

Expected behavior

I would have expected the first key to remain unchanged (with the leading zero)
dict_keys([('01',), ('0010',), ('10',), ('foo',)])

Installed versions

Broken on 1.8.1. This used to work on 1.7.1.

--------Version info---------
Polars:              1.8.1
Index type:          UInt32
Platform:            Linux-4.18.0-372.9.1.el8.x86_64-x86_64-with-glibc2.28
Python:              3.11.9 | packaged by conda-forge | (main, Apr 19 2024, 18:36:13) [GCC 12.3.0]
----Optional dependencies----
adbc_driver_manager  <not installed>
altair               <not installed>
cloudpickle          2.2.1
connectorx           0.3.3
deltalake            0.18.2
fastexcel            <not installed>
fsspec               2024.6.1
gevent               <not installed>
great_tables         0.10.0
matplotlib           3.9.1
nest_asyncio         1.6.0
numpy                1.24.4
openpyxl             3.1.5
pandas               2.1.4
pyarrow              16.1.0
pydantic             2.8.2
pyiceberg            <not installed>
sqlalchemy           2.0.32
torch                2.3.1.post100
xlsx2csv             <not installed>
xlsxwriter           <not installed>

[coastalwhite]

I can reproduce on 1.8.1 but not on main anymore. I think this is already fixed as part of #18888.

[ritchie46]

Fixed by #18893

[ritchie46]

Will patch tonight.

[ptomecek]

Thanks everyone, appreciate the speedy response!