[Python] Possible to calculate counts and percentage in one chain using polars?

From seeing some of the other polars answers it seems most things can be complete in a single chain. Is that possible with the below example? Any simplifications possible?

import polars as pl
scores = pl.DataFrame({
'zone': ['North', 'North', 'North', 'South', 'East', 'East', 'East', 'East'],
'score': [78, 39, 76, 56, 67, 89, 100, 55]
})

cnt = scores.group_by("zone").len()
cnt.with_columns(
(100 * pl.col("len") / pl.col("len").sum())
.round(2)
.cast(str)
.str.replace(r"$", "%")
.alias("perc")
)


shape: (3, 3)
┌───────┬─────┬───────┐
│ zone ┆ len ┆ perc │
│ --- ┆ --- ┆ --- │
│ str ┆ u32 ┆ str │
╞═══════╪═════╪═══════╡
│ South ┆ 1 ┆ 12.5% │
│ East ┆ 4 ┆ 50.0% │
│ North ┆ 3 ┆ 37.5% │
└───────┴─────┴───────┘

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