# Polars 1.42.1 — Python Polars 1.42.1

- Product: Polars (https://whatsnew.fyi/product/polars)
- Vendor: Polars
- Date: 2026-06-30
- Version: 1.42.1
- Original notes: https://github.com/pola-rs/polars/releases/tag/py-1.42.1
- Permalink: https://whatsnew.fyi/product/polars/releases/1.42.1

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- **deprecated** — Deprecate strict parameter of pl.concat, replace with new how='horizontal_extend'
- **changed** — Add a sampled resolve mode for multi-file parquet metadata
- **changed** — Speed up small dtype series sums with a upcast sum kernel
- **changed** — Don't block on path expansion
- **fixed** — Fix incorrect sorted fast-path returning nan for grouped max
- **fixed** — Fix panic on scan_parquet filter of fixed-size binary column
- **fixed** — Fix decimal dynamic float cast
- **fixed** — Fix pyiceberg key dot HDFS prefix filter
- **fixed** — Fix projection pushdown panic on select(len()) after groupby
- **fixed** — Fully resolve remaining ResourceWarning leaks in database and iceberg tests
- **fixed** — Fix expiry time loading for AWS DeferredRefreshableCredentials
- **fixed** — Avoid panic on temporal extraction for datetime columns with nulls
- **fixed** — Prevent panic in replace when old or new contain Expr or object dtype values

##### ⚠️ Deprecations

- Deprecate `strict` parameter of `pl.concat`, replace with new `how='horizontal_extend'` (#27965)

##### 🚀 Performance improvements

- Add a sampled resolve mode for multi-file parquet metadata (#28111)
- Speed up small dtype series sums with a upcast sum kernel (#27958)
- Don't block on path expansion (#28073)

##### ✨ Enhancements

- Close ResourceWarning leaks in database tests (#28066)

##### 🐞 Bug fixes

- Incorrect sorted fast-path returning nan for grouped max (#28129)
- Fix panic on scan\_parquet filter of fixed-size binary column (#28122)
- Fix decimal dynamic float cast (#28126)
- Fix pyiceberg key dot HDFS prefix filter (#28109)
- Fix projection pushdown panic on `select(len())` after `groupby` (#28108)
- Fully resolve remaining `ResourceWarning` leaks in database/iceberg tests (#28107)
- Expiry time loading for AWS `DeferredRefreshableCredentials` (#28099)
- Close ResourceWarning leaks in database tests (#28066)
- Avoid panic on temporal extraction for datetime columns with nulls (#28054)
- Prevent panic in `replace` when `old`/`new` contain Expr or object dtype values (#27433)

##### 📖 Documentation

- Fix dataset regression in the examples (#28131)
- Emphasize to generally not ever write Rust tests (#28082)
- Mention Polars skill in User Guide's LLM section (#28113)

##### 🛠️ Other improvements

- Disallow usage of `tokio::spawn` in clippy (#28123)
- Improve `Makefile` with respect to `venv` robustness (#28110)
- Remove legacy prelude glob imports from leaf files (#28114)
- Skip pandas 3.0.4 due to `pd.TimeDelta` segfault (#28125)
- Update `mypy` to the new `2.x` release (#28116)
- Ensure `pyrefly` checks run as part of `make pre-commit` (#28095)
- Fix `test_select_explode_height_filter_order_by` failure when `POLARS_MAX_THREADS=2` (#28090)
- Add Morsel::height (#28060)

Thank you to all our contributors for making this release possible!
@0guban0v, @Kevin-Patyk, @TNieuwdorp, @alexander-beedie, @azimafroozeh, @dsprenkels, @kdn36, @nameexhaustion, @orlp, @raphaelroshan, @ritchie46 and @sar-cheng