py-1.42.0

## ⚠️ Deprecations

- Deprecate casts from string to temporal dtypes (#28056)

## 🚀 Performance improvements

- Add bytes-based concurrency control for cloud IO (#27924)
- Stop flushing multiplexer on phase change (#28013)
- Prevent empty chunks from triggering copy in rechunk (#27953)
- Improve performance of struct unnest inside list eval on streaming (#27905)
- Eliminate filters with contradictory predicates (#27775)

## ✨ Enhancements

- Deprecate casts from string to temporal dtypes (#28056)
- Add naive out-of-core spilling to Polars (#27998)
- Add experimental strict mode (#28023)
- Optimize non-negative len and null\_count comparisons (#28002)
- Optimize len and null\_count comparisons (#27727)
- Support SQL's implicit `JOIN` syntax (#27890)
- Add `Expr.is_sorted` (#26708)
- Add suggestions in wrong api usage or mismatched column names (#27954)
- Add external object\_store support for non-native schemes (#27871)
- Skip Delta files and parquet row groups using per-field struct statistics (#27887)
- Improve IR sortedness detection for with\_row\_index and explode (#27875)
- Add `DataFrame.is_sorted()` (#27870)
- Expose fixed-size rolling window expressions in Python visitor (#27108)
- Fix SchemaError using lazy HConcat->Sink (#27770)
- Add tiered multi-file parquet metadata resolver (#27720)
- Cache and shuffle DNS for cloud object\_store (#27659)

## 🐞 Bug fixes

- Add a deprecation warning for `.explode()` without `empty_as_null` argument (#28040)
- Fix `select(len())` incorrectly returned 0 when using `scan_iceberg` with `pyiceberg` as reader override (#28044)
- Ensure slice expr always observes input order (#28041)
- Fix projection pushdown with row index out of order (#28043)
- Fix cross-join predicates not applied when using `sink_*` functions (#28042)
- Grammar corrections (recommend to → recommend, allows to → allows using) (#28038)
- Ensure optimisations aren't omitted by cached IR nodes (#28004)
- Computed GROUP keys in SQL projections (#27989)
- Handle empty DataFrames in `dt.truncate` and `dt.round` (#26120)
- Address join alias state leakage in SQL CTEs (#27985)
- Support scanning `file://` URIs with percent-encoded paths (#27876)
- Lower SQL `[NOT] IN (subquery)` to semi/anti join (#27888)
- Check for continuity across morsels in AsOf join node (#27461)
- Add test for projection pushdown with hconcat regression (#27937)
- Traverse caches only once in explain (#27939)
- Preserve null placement when collapsing `sort.reverse()` into single sort (#27918)
- Incorrect schema order for hstack in projection pushdown optimizer (#27920)
- Fix duplicated map\_elements warning on streaming engine (#27919)
- Use block\_in\_place\_on for calls which can come from executor thread (#27855)
- Mismatch in max\_threads -> pipeline configuration (#27854)
- Keep maintain\_order on sliced unique (#27852)
- Fix SchemaError using lazy HConcat->Sink (#27770)
- Fix incorrect projection height when selecting only literals (#27825)
- Select with expr slice and len gave incorrect len (#27824)
- Prevent import panic when environment variable set to unexpected value (#27831)

## 📖 Documentation

- New On-Prem release (#27979)
- Add note on OOM behavior on Kubernetes (#27972)
- Properly render backslashes in CSV `eol_char` docstrings (#27962)
- Add entry for `DataFrame.is_sorted()` (#27913)
- Clarify compat\_level export docs (#27715)
- Add robots.txt disallowing stale docs and added sitemap for better SEO (#27901)
- Update Polars \<> Spark comparison (#27873)
- Bump to patched version (#27851)
- Replace Typeform sign-up URL with new enterprise link (#27838)
- Correct wrong head call (#27848)
- Add Polars On-Prem 0.5.0 release (#27849)
- Correct onprem license helm values (#27847)
- Update connecting Polars Cloud to AWS documentation (#27823)
- Correct cost/connectivity sections (#27813)
- Add sections about egress (#27805)
- Tragic typo in On-Prem docs (#27804)

## 🛠️ Other improvements

- Add AI agent disclsoure (#28064)
- Bump memmap2 version (#28050)
- Update `sqlparser` dependency (#28021)
- Update `pyo3` and `rust-numpy` to `0.29.0` (#27970)
- Add `2.0` branch as primary branch (#27978)
- Patch jemalloc-sys for Makefile bug (#27945)
- Restore Cargo.lock (#27964)
- Add test for projection pushdown with hconcat regression (#27937)
- Update `deny.toml` configuration (#27949)
- Doctest skip refactor and add hugging face rate limited tests (#27885)
- Run Pyrefly type-checker on source code (#27722)
- Bump Rust dependencies (#27874)
- Changes needed for Rust 0.54.x (#27853)
- Use `Vec` instead of `PlHashMap` for `ProjectionInfo.map` (#27856)
- Reduce `codegen-units` (#27835)
- Refactor to avoid `unbound-name` Pyright/Pyrefly errors (#27827)

Thank you to all our contributors for making this release possible!
@0guban0v, @April-Sonnet, @BitWeaverDev, @EndPositive, @JakubValtar, @Kevin-Patyk, @Liyixin95, @MarcoGorelli, @Matt711, @TNieuwdorp, @alexander-beedie, @ankane, @azimafroozeh, @cBournhonesque, @carnarez, @dsprenkels, @gautamvarmadatla, @kdn36, @nameexhaustion, @orlp, @ritchie46, @tolleybot, @toreerdmann, @uurl and @xixixao