map_groups panic if function requires positional arguments #26647
Description
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(x=1).group_by("x").map_groups(lambda x, y: x)
# PanicException: UDF failed: <lambda>() missing 1 required positional argument: 'y'Log output
thread '<unnamed>' (2397467) panicked at crates/polars-python/src/dataframe/general.rs:393:35:
UDF failed: <lambda>() missing 1 required positional argument: 'y'Issue description
Called the wrong function by mistake.
Seems like it just needs to propagate the error instead of a panic.
Expected behavior
Error instead of panic.
Installed versions
Details
--------Version info---------
Polars: 1.38.1
Index type: UInt32
Platform: macOS-13.6.1-arm64-arm-64bit-Mach-O
Python: 3.13.3 (main, Apr 8 2025, 13:54:08) [Clang 15.0.0 (clang-1500.1.0.2.5)]
Runtime: rt32
----Optional dependencies----
Azure CLI <not installed>
adbc_driver_manager 1.10.0
altair 6.0.0
azure.identity 1.25.1
boto3 1.42.42
cloudpickle 3.1.2
connectorx 0.4.5
deltalake 1.4.2
fastexcel 0.19.0
fsspec 2026.2.0
gevent 25.9.1
google.auth 2.48.0
great_tables 0.20.0
matplotlib 3.10.8
numpy 2.3.5
openpyxl 3.1.5
pandas 3.0.0
polars_cloud 0.4.3
pyarrow 23.0.0
pydantic 2.12.5
pyiceberg 0.10.0
sqlalchemy 2.0.46
torch <not installed>
xlsx2csv 0.8.6
xlsxwriter 3.2.9