Python Polars 0.18.1

🏆 Highlights

• add dedicated selectors module, consolidating/expanding existing selector capabilities (#9204)

🚀 Performance improvements

• slightly improve n_unique performance (#9286)
• use ciborium in Expression pickling (#9235)

✨ Enhancements

• add join cardinality validation (#9278)
• implement set operations for selector API (#9276)
• keep sorted flag after Expr::truncate (#9275)
• add "sql_expr" function (#9248)
• rewrite correlation functions to expression architecture (#9258)
• keep sorted flag on offset_by (#9253)
• add expression json serde (#9236)
• add intersection primitive for selector API (#9240)
• building blocks for expression expansion sets (#9231)
• Add ddof option to rolling_var and rolling_std (#8957)
• immediately flatten nested unions (#9220)
• Allow empty select/with_columns/groupby (#9205)
• add a datetime selector (#9212)
• support float expression on integers (#9210)
• add dedicated selectors module, consolidating/expanding existing selector capabilities (#9204)
• add binary to list<u8> cast (#9161)
• groupby_dynamic by quarter. (#6842)
• add arr.unique expression (#9159)
• implement explode for DataType::Array (#9157)
• Decimal type: sum, min, max aggregations in select and agg context. (#9135)
• Decimal arithmetic (#9123)
• support decimals as cast types in csv parser (#9121)
• Improve error handling for repeat (#9117)

🐞 Bug fixes

• fix pyarrow dataset literal filter (#9274)
• raise on invalid sort_by (#9262)
• match missing Array and Struct classes in FromPyObject (#9271)
• correct ne/e_missing schema (#9257)
• fix cached reproject offsets (#9254)
• delay opening files in streaming engine (#9251)
• ensure agg(F(lit)) == lit (#9222)
• don't SO on concat(expressions) (#9214)
• df.apply first rechunk (#9211)
• clip window_size to length in rolling_apply (#9209)
• raise error on invalid df.apply return (#9207)
• Handle edge cases of named select input (#9198)
• rolling_apply window_size == len (#9181)
• respect time zone in strptime/to_datetime when exact=False (#9171)
• make null chunking behavior equal to other dtypes (#9176)
• return single numpy array in Array dtype -> numpy (#9164)
• fix regression in boolean nulls comparison (#9142)
• fix struct null_count if fields are null arrays (#9151)
• Fix DataFrame.to_arrow() for 0x0 dataframes (#9144)
• categorical construction from null values (#9145)
• let apply caller determine if length needs to be checked. (#9140)
• struct is_in should upcast numeric types (#9110)
• Restore functionality of name arg for date_range (#9107)
• bubble up dtype when converting from arrow (#9120)

🛠️ Other improvements

• Fix grammar and add periods in Expr.over docs (#9244)
• Update linting for py-polars crate (#9242)
• Deprecate exprs=... input for select/with_columns/agg/struct (#9219)
• Enable parallelization in Python Windows tests (#9232)
• Use pytest tmp_path (#9206)
• Build docs in parallel (#9229)
• Unify Python docs workflows (#9228)
• add docstring to __array__ methods (#8055)
• Update expr parsing util to return PyExpr (#9166)
• update pyo3 requirement from 0.18 to 0.19 (#9155)
• clarify how the windows are formed in the rolling_* functions (#9192)
• stabilise polars importtime check (#9196)
• fix "to_decimal" docstring (#9197)
• note that exact=False is a performance footgun (#9186)
• change decimal inference and argument order (#9133)
• Cache Rust build on main branch (#9130)
• Improve df.clear() docs (#8809)
• Bump maturin to 1.0.1 (#9115)
• Bump lint dependency versions (#9116)

Thank you to all our contributors for making this release possible!
@DeflateAwning, @MarcoGorelli, @alexander-beedie, @ankane, @avimallu, @bfeif, @dependabot, @dependabot[bot], @jonashaag, @josh, @lorentzenchr, @magarick, @ritchie46, @stinodego, @universalmind303 and @zundertj