hash() list of string PanicException

[cmdlineluser]

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

import polars as pl

pl.select(pl.lit(["foo"]).hash())
# PanicException: Hashing a list with a non-numeric inner type not supported. Got dtype: List(String)

Log output

thread '<unnamed>' panicked at crates/polars-ops/src/chunked_array/list/hash.rs:49:9:
Hashing a list with a non-numeric inner type not supported. Got dtype: List(String)

Issue description

I think it's just a matter of propagating the error message.

We can cast to Categorical before hashing.

pl.select(pl.lit(["foo"]).cast(pl.List(pl.Categorical)).hash())
# shape: (1, 1)
# ┌─────────────────────┐
# │ literal             │
# │ ---                 │
# │ u64                 │
# ╞═════════════════════╡
# │ 2451233427067226091 │
# └─────────────────────┘

Expected behavior

No panic.

Installed versions

--------Version info---------
Polars:              1.23.0
Index type:          UInt32
Platform:            macOS-13.6.1-arm64-arm-64bit-Mach-O
Python:              3.13.0 (main, Oct  7 2024, 05:02:14) [Clang 15.0.0 (clang-1500.1.0.2.5)]
LTS CPU:             False

----Optional dependencies----
adbc_driver_manager  <not installed>
altair               <not installed>
boto3                <not installed>
cloudpickle          <not installed>
connectorx           <not installed>
deltalake            <not installed>
fastexcel            0.12.0
fsspec               <not installed>
gevent               <not installed>
google.auth          <not installed>
great_tables         0.14.0
matplotlib           <not installed>
nest_asyncio         <not installed>
numpy                2.1.3
openpyxl             3.1.5
pandas               2.2.3
pyarrow              18.0.0
pydantic             <not installed>
pyiceberg            <not installed>
sqlalchemy           <not installed>
torch                <not installed>
xlsx2csv             <not installed>
xlsxwriter           3.2.0

[mcrumiller]

We can cast to Categorical before hashing.

You can, but I'd be careful with that, the hash of the categorical is simply the hash of the underlying physical representation and is completely independent of the string.

>>> import polars as pl
>>> pl.Series(["test"], dtype=pl.Categorical).hash()
Series: '' [u64]
[
        16718381540940362211
]
>>> pl.Series(["Completely different string"], dtype=pl.Categorical).hash()
Series: '' [u64]
[
        16718381540940362211
]
>>> pl.Series(["yet another string"], dtype=pl.Categorical).hash()
Series: '' [u64]
[
        16718381540940362211
]

These series were not created within the same global string cache, and so they each have independent physical representations that start with 0. So you get this:

s1 = pl.Series(["first string"], dtype=pl.Categorical)
s2 = pl.Series(["a new different string"], dtype=pl.Categorical)
s1.hash() == s2.hash()
Series: '' [bool]
[
        true
]