# Polars 1.40.0 — Python Polars 1.40.0

- Product: Polars (https://whatsnew.fyi/product/polars)
- Vendor: Polars
- Date: 2026-04-18
- Version: 1.40.0
- Original notes: https://github.com/pola-rs/polars/releases/tag/py-1.40.0
- Permalink: https://whatsnew.fyi/product/polars/releases/1.40.0

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

---

- **added** — Add streaming support for grouped AsOf join
- **added** — Add `ignore_nulls` to `{list,arr}.{any,all}`
- **added** — Add `is_unique` to list/array dtypes
- **added** — Add `pl.merge_sorted` operating on multiple frames
- **added** — Add native streaming `interpolate`
- **changed** — Create IR slice from expr slice pushdown
- **changed** — Avoid unnecessary rechunk when sorting already sorted DataFrame
- **changed** — Lower basic over() to streaming primitives
- **changed** — Lower `drop_{nulls,nans}` in streaming `group_by` aggregations
- **changed** — Lower `entropy` to streaming reductions
- **changed** — Streaming `strptime` with `format=None`
- **changed** — Lower `skew` / `kurtosis` to streaming aggregations
- **changed** — Post apply pyarrow filter in Polars' engine instead of pyarrow
- **changed** — Optimize `drop_nulls().{first,last}()` to `{first,last}(ignore_nulls=True)`
- **changed** — Always process pyarrow scan in batches
- **changed** — Make `cut` output `Enum` and mark as elementwise
- **changed** — Use delta stats for mixed hive and non-hive predicate pushdown
- **changed** — Take into account size per row in join sampling
- **changed** — Streaming is_first_distinct and unique(maintain_order=True)
- **changed** — Streaming `cov` and `corr`

##### 🏆 Highlights

- Add streaming support for grouped AsOf join (#27293)

##### ⚠️ Deprecations

- Deprecate support for dataframe interchange protocol (#27214)

##### 🚀 Performance improvements

- Create IR slice from expr slice pushdown (#27200)
- Add streaming support for grouped AsOf join (#27293)
- Avoid unnecessary rechunk when sorting already sorted DataFrame (#27264)
- Lower basic over() to streaming primitives (#27303)
- Lower `drop_{nulls,nans}` in streaming `group_by` aggregations (#27296)
- Lower `entropy` to streaming reductions (#27174)
- Add native streaming `interpolate` (#27185)
- Streaming `strptime` with `format=None` (#27056)
- Lower `skew` / `kurtosis` to streaming aggregations (#27176)
- Post apply pyarrow filter in Polars' engine instead of pyarrow (#27192)
- Optimize `drop_nulls().{first,last}()` to `{first,last}(ignore_nulls=True)` (#27187)
- Always process pyarrow scan in batches (#27183)
- Make `cut` output `Enum` and mark as elementwise (#27173)
- Remove unused expression sorts (#27075)
- Use delta stats for mixed hive and non-hive predicate pushdown (#27102)
- Take into account size per row in join sampling (#27098)
- Streaming is\_first\_distinct and unique(maintain\_order=True) (#27052)
- Streaming `cov` and `corr` (#27008)
- Add sorted unique node to streaming engine (#26990)
- Ensure Expr.append is lowered in streaming engine (#27022)
- Collapse consecutive Sort nodes (#26965)
- Drop `maintain_order=True` requirement in `sink_delta` (#27007)

##### ✨ Enhancements

- Add `ignore_nulls` to `{list,arr}.{any,all}` (#27186)
- Lock-free memory manager with spill-to-disk and fully OOC multiplexer (#26774)
- Add `is_unique` to list/array dtypes (#27290)
- Streaming pyarrow datasets sources (#27230)
- Add `pl.merge_sorted` operating on multiple frames (#27014)
- Allow `group_by()` without key exprs (#27141)
- Change default scan/read\_lines column name from "lines" to "line" (#27122)
- Make unnest() effective on all columns by default (#27029)
- Collapse consecutive Sort nodes (#26965)

##### 🐞 Bug fixes

- Update `groups` to correct length for `Implode` (#27282)
- Fix scan\_csv missing\_columns='insert' overwrote existing data with NULLs (#27297)
- Raise on non-numeric inputs in `pl.int_ranges` (#27294)
- Fix always-true filter conversion to Iceberg filter (#27119)
- Do not skip nulls when enumerating over rows in grouped AsOf join (#27275)
- Fix `pivot` dropping data for null `on` values (#27273)
- Resolve multiple files deadlock in CSV async reader (#27073)
- Widen decimal precision on sum aggregation (#27270)
- Correct lf.remote type (#27261)
- Default `LazyFrame.map_batches` to no optimizations (#27262)
- Extend `StructEval` schema context in `StackOptimizer` (#27243)
- Preserve nulls when casting from all-null `Series` to `Struct` (#27241)
- Fix `scan_delta` filter on empty dataframe (#27244)
- Prevent `DataFrame` creation panic on `list[struct]` with heterogenous types (#27217)
- Named aggregation `__structify` was being ignored (#27148)
- Skip `null` group entries when collecting AsOf-by groups (#27215)
- Fix panic with empty order\_by in over expression (#27088)
- Write field ID from `sink_parquet` (#27196)
- Fix statistics for Null columns in Parquet (#27021)
- Do not prune sort nodes containing slice with dyn predicate (#27140)
- Correct grouped `Binary` `arg_min`/`arg_max` and `String` single-element arg indices (#27172)
- Resolve multiple files deadlock in NDJSON async reader (#27204)
- Overflow panic in interpolate nearest (#27205)
- Using checked arithmetic in `int96_to_i64_ns` to prevent overflow panic (#27129)
- Don't trigger csv fast count if predicate is pushed down (#27190)
- Support all integer dtypes for Series index assignment (#27188)
- Streaming sort by-expressions were lowered incorrectly (#27158)
- Replace multiprocessing.dummy.Pool with ThreadPoolExecutor (#27175)
- Reset IO metrics instead of consuming (#27156)
- Output SVG if output\_path ends with '.svg' in show\_grap

_[Truncated at 4000 characters — full notes: https://github.com/pola-rs/polars/releases/tag/py-1.40.0]_