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Reproducible example

import polars as pl

def function(s: pl.Series, a: int, b: int = 0) -> pl.Series:
    return a * s + b

df = pl.DataFrame({"a": [1, 2]})
df.map_columns("a", function, 1, b=2)

Log output

Issue description

The type hint for the function parameter in DataFrame.map_columns is currently Callable[[Series], Series]. However, the implementation of map_columns passes *args and **kwargs from the map_columns method directly to the function callable. This makes the current type hint incorrect and overly restrictive, as it implies the function only accepts a single Series argument.

To accurately reflect the function's usage, the type hint for function should be updated to Callable[Concatenate[Series, P], Series], where P is a ParamSpec capturing the *args and **kwargs passed to map_columns. This change would ensure that the type hint correctly indicates that the user-provided function can accept additional positional and keyword arguments.

Expected behavior

Type checkers (e.g., MyPy) should correctly recognize that the function parameter of DataFrame.map_columns can accept additional positional and keyword arguments (*args, **kwargs) after the initial Series argument. This ensures that custom functions passed to map_columns can be type-checked accurately when they utilize these additional arguments.

Installed versions

--------Version info---------
Polars:              1.37.1
Index type:          UInt32
Platform:            Windows-11-10.0.26200-SP0
Python:              3.14.2 (main, Dec  9 2025, 19:03:14) [MSC v.1944 64 bit (AMD64)]
Runtime:             rt32

----Optional dependencies----
Azure CLI            <not installed>
adbc_driver_manager  <not installed>
altair               <not installed>
azure.identity       <not installed>
boto3                <not installed>
cloudpickle          <not installed>
connectorx           <not installed>
deltalake            <not installed>
fastexcel            <not installed>
fsspec               <not installed>
gevent               <not installed>
google.auth          <not installed>
great_tables         <not installed>
matplotlib           <not installed>
numpy                <not installed>
openpyxl             <not installed>
pandas               <not installed>
polars_cloud         <not installed>
pyarrow              <not installed>
pydantic             <not installed>
pyiceberg            <not installed>
sqlalchemy           <not installed>
torch                <not installed>
xlsx2csv             <not installed>
xlsxwriter           <not installed>