you have map_elements in polars which does exactly this.

https://docs.pola.rs/api/python/dev/reference/expressions/ap...

You can also iter_rows into a lambda if you really want to.

https://docs.pola.rs/api/python/stable/reference/dataframe/a...

Personally I find it extremely rare that I need to do this given Polars expressions are so comprehensive, including when.then.otherwise when all else fails.