pola-rs/polars: Python polars 0.18.1

🏆 Highlights

add dedicated selectors module, consolidating/expanding existing selector capabilities ([#9204](https://github.com/pola-rs/polars/pull/9204))

🚀 Performance improvements

slightly improve n_unique performance ([#9286](https://github.com/pola-rs/polars/pull/9286))
use ciborium in Expression pickling ([#9235](https://github.com/pola-rs/polars/pull/9235))

✨ Enhancements

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

🐞 Bug fixes

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

🛠️ Other improvements

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