Polars aggregate without a groupby

Is there a way to call .agg() without grouping first? I want to perform standard aggregations but only want one row in the response, rather than separate rows for separate groups.

I could do something like

df.with_columns(dummy_col=pl.lit("dummy_col")).group_by('dummy_col').agg(<aggregateion>)

but I'm wondering if there's a way without the dummy stuff