# Polars 1.27.0 — Python Polars 1.27.0

- Product: Polars (https://whatsnew.fyi/product/polars)
- Vendor: Polars
- Date: 2025-04-09
- Version: 1.27.0
- Original notes: https://github.com/pola-rs/polars/releases/tag/py-1.27.0
- Permalink: https://whatsnew.fyi/product/polars/releases/1.27.0

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'.

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- **changed** — Make bottom interval closed in hist
- **changed** — Change Partition API to base_path and file_path
- **added** — Add SPLIT_PART string function to the SQL interface
- **changed** — Allow scalar expr in Expr.diff
- **added** — Support additional unsigned int aliases in the SQL interface
- **added** — Add STRING_TO_ARRAY function to the SQL interface
- **added** — Add dt.is_business_day
- **added** — Add an eager parameter to pl.cov
- **added** — Add support for Int128 parsing and recognition to the SQL interface
- **added** — Add an eager parameter to pl.coalesce
- **added** — Add an eager parameter to pl.corr
- **added** — Allow sinking to abstract python io and fs classes
- **added** — Add add_alp_optimize_exprs to IRBuilder
- **added** — Add cat.slice
- **changed** — Support growing schema if line length increases during csv schema inference
- **changed** — Replace thread unsafe GilOnceCell with Mutex
- **changed** — Support modified dsl in file cache
- **fixed** — Implode in agg
- **deprecated** — Deprecate duplicate backward_fill and forward_fill interface

##### 💥 Breaking changes

- Make bottom interval closed in `hist` (#22090)
- Change Partition API to `base_path` and `file_path` (#21888)

##### 🚀 Performance improvements

- Add CSE to streaming groupby (#22196)
- Speed-up new streaming predicate filtering (#22179)
- Speedup new-streaming file row count (#22169)
- Fix quadratic behavior when casting Enums (#22008)
- Lower is\_in to bitmap-output semi-join in new streaming engine (#21948)
- Fast path for empty inner join (#21965)
- Add native semi/anti join in new streaming engine (#21937)
- Cache regex compilation globally (#21929)

##### ✨ Enhancements

- Add `SPLIT_PART` string function to the SQL interface (#22158)
- Allow scalar expr in `Expr.diff` (#22142)
- Support additional unsigned int aliases in the SQL interface (#22127)
- Add `STRING_TO_ARRAY` function to the SQL interface (#22129)
- Add dt.is\_business\_day (#21776)
- Add an `eager` parameter to `pl.cov` (#22098)
- Add support for `Int128` parsing/recognition to the SQL interface (#22104)
- Add an `eager` parameter to `pl.coalesce` (#22092)
- Add an `eager` parameter to `pl.corr` (#22097)
- Allow sinking to abstract python `io` and `fs` classes (#21987)
- Add `add_alp_optimize_exprs` to `IRBuilder` (#22061)
- Add `cat.slice` (#21971)
- Support growing schema if line lenght increases during csv schema inference (#21979)
- Replace thread unsafe `GilOnceCell` with `Mutex` (#21927)
- Support modified dsl in file cache (#21907)

##### 🐞 Bug fixes

- Implode in agg (#22197)
- Reduce GIL hold time for IO plugins in new-streaming (#22186)
- Enhance predicate validation and cast safety in `join_where` (#22112)
- Handle Parquet with compressed empty DataPage v2 (#22172)
- Schema error during lowering (#22175)
- Rewrite unroll of overlapping groups to mitigate out of range index panic (#22072)
- Incorrect rounding for very large/small numbers (#22173)
- Allow set input to `list.set_*` operations (#22163)
- Deadlock in join due to rayon nested task-stealing (#22159)
- Mark `Expr.repeat_by` as elementwise (#22068)
- Fix csv serializer panic by supporting ScalarColumn in as\_single\_chunk (#22146)
- Raise an error if a number doesn't have associated unit in duration strings (#22035)
- Add `i128` as supertype to boolean (#22138)
- Fix panic when constructing DF from pyarrow due to duplicate field names (#22114)
- Add broadcasts and error messages for many elementwise operations (#22130)
- Throw error for `n=0` on `list.gather_every` (#22122)
- Throw error for unsupported rolling operations (#22121)
- Error on unequal length `str.to_integer` arguments (#22100)
- Make bottom interval closed in `hist` (#22090)
- Relative path resolution for plugin libraries (#21911)
- Avoiding panic with striptime for out-of-bounds dates (#21208)
- Join revmaps for categoricals in `merge_sorted` (#21976)
- Fix glob expansion matching extra files (#21991)
- Ensure SQL dot-notation for nested column fields resolves correctly (#22109)
- Parquet filter performance regression from multiscan dispatch (#22116)
- Panic for unequal length `ewm_mean_by` args (#22093)
- Add scalarity checks to `pl.repeat` (#22088)
- Type check `n` parameter of `pl.repeat` (#22071)
- Mark `bitwise_{count,leading,trailing}_{ones,zeros}` as elementwise (#22044)
- Mark `pl.*_ranges` functions correctly as element-wise (#22059)
- Correctly type check `pl.arctan2` (#22060)
- Mark `pl.business_day_count` as elementwise (#22055)
- Check input python type for `str.extract_groups` (#22032)
- Check types for `fill_char` in `str.pad_{start,end}` (#22036)
- Mark `str.to_decimal` properly as non-elementwise (#22040)
- Documented return type for `bin.encode` and `bin.decode` (#22022)
- Revert #22017 and improve block(\_in\_place)\_on doc comment (#22031)
- Remove outdated depth warning (#22030)
- Expression pl.concat was incorrectly marked as elementwise (#22019)
- Use block\_in\_place\_on to start streaming (#22017)
- Panic on empty aggregation in streaming (#22016)
- Error instead of

_[Truncated at 4000 characters — full notes: https://github.com/pola-rs/polars/releases/tag/py-1.27.0]_