Column selections inside `list.eval` 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

df = pl.DataFrame({"x": [[1, 2]]})

df.select(pl.col("x").list.eval(pl.exclude("")))
# PanicException: index out of bounds: the len is 0 but the index is 0

Log output

␤

Issue description

Testing various expressions after reading the question from StackOverflow¹ asking about pl.all() usage inside list.eval().

It seems only pl.col("name") is disallowed.

df.select(pl.col("x").list.eval(pl.col(pl.String)))
# PanicException: index out of bounds: the len is 0 but the index is 0

Various things seem to be allowed and end up treated the same as pl.element()

df.select(pl.col("x").list.eval(pl.exclude("im-not-here")))
df.select(pl.col("x").list.eval(pl.col(pl.Int64)))
df.select(pl.col("x").list.eval(pl.exclude("x")))
df.select(pl.col("x").list.eval(pl.nth(-1)))

# shape: (1, 1)
# ┌───────────┐
# │ x         │
# │ ---       │
# │ list[i64] │
# ╞═══════════╡
# │ [1, 2]    │
# └───────────┘

AFAIK .pivot() is the other place that allows pl.element() - it seems to disallow all the cases I've tried.

(It does allow pl.all() to be used instead of pl.element())

Expected behavior

No panic.

Installed versions

--------Version info---------
Polars:              1.29.0
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

Footnotes

1. https://stackoverflow.com/questions/79619760/ ↩

[cmdlineluser]

Just testing again after the #22911 update.

non-existing exclude / nth now raise an appropriate error.

df.select(pl.col("x").list.eval(pl.nth(-1)))
df.select(pl.col("x").list.eval(pl.exclude("im-not-here")))
# ComputeError: named columns are not allowed in `list.eval`; consider using `element` or `col("")`

The others now result in an empty frame instead of a panic.

df.select(pl.col("x").list.eval(pl.exclude("x")))
# shape: (0, 0)
# ┌┐
# ╞╡
# └┘

df.select(pl.col("x").list.eval(pl.col(pl.String)))
# shape: (0, 0)
# ┌┐
# ╞╡
# └┘