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docs: add CHANGELOG and release announcement for v1.17
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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‎CHANGELOG.md‎

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# Changelog — python-mip 1.17
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> Changes since **1.15.0** (1.16 was an unreleased RC)
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---
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## New Features
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### HiGHS Solver Support
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python-mip now ships with full support for the [HiGHS](https://highs.dev) open-source solver as a
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first-class backend (alongside CBC and Gurobi). HiGHS is a high-performance solver for LP and MIP
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problems with a permissive MIT licence.
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Key capabilities added:
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- Full LP and MIP solve via HiGHS C API (through `highsbox`)
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- Warm-start (basis handoff) for LP re-solves
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- `relax=True` support in `optimize()`
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- Variable and constraint inspection/modification
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- Correct handling of `UNBOUNDED` vs `INFEASIBLE` status
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- Reduced memory footprint and improved file read/write consistency
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HiGHS is installed as an optional dependency: `pip install mip[highs]`.
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### macOS Apple Silicon (M1/M2/M3) Native Support
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CBC now runs natively on Apple Silicon via a pre-built ARM64 binary, replacing the previous
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Rosetta 2 x86_64 fallback.
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---
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## Infrastructure & Distribution
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### CBC Binaries via `cbcbox`
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The bundled CBC shared libraries (`.so`, `.dylib`, `.dll`) have been **removed from the
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python-mip source tree**. CBC binaries are now distributed through the
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[cbcbox](https://pypi.org/project/cbcbox/) PyPI package, which provides pre-built wheels for:
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- Linux x86\_64 and aarch64 (ARM64)
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- macOS x86\_64 and arm64
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- Windows x64
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`cbcbox` is a dedicated package whose sole job is to ship up-to-date CBC binaries for all
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major platforms. This decoupling means future CBC upgrades are released without touching
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python-mip itself. The minimum required version is `cbcbox>=2.902`.
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### Automated PyPI Publishing
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A new GitHub Actions workflow (`.github/workflows/publish.yml`) automatically publishes to
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PyPI whenever a `v*` tag is pushed. It uses OIDC Trusted Publisher authentication — no API
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tokens to rotate.
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### Modernised CI Matrix
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| Platform | OS |
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|---|---|
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| Linux x86\_64 | ubuntu-24.04 |
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| Linux aarch64 | ubuntu-24.04-arm *(new)* |
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| macOS ARM64 | macos-15 *(new)* |
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| Windows x64 | windows-2025 *(new)* |
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Python versions tested: **3.10, 3.11, 3.12, 3.13, PyPy 3.11**.
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---
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## Bug Fixes
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- **CBC re-solve correctness**: A bug introduced by newer CBC versions caused stale solution
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data to be returned when `optimize()` was called multiple times on the same model. Fixed by
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calling `Cbc_reset()` before each `Cbc_solve()`, with objective sense saved and restored
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around the reset.
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- **`isfile` import missing in `SolverCbc.read()`**: `os.path.isfile` was used but not
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imported, causing a `NameError` when loading a model from a file.
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- **Windows DLL loading**: On Python 3.8+, Windows ignores `PATH` when resolving DLL
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dependencies. Fixed by calling `os.add_dll_directory()` on the cbcbox `bin/` directory.
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- **Empty `LinExpr` in constraints**: Constraints containing an empty linear expression were
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not handled correctly. Fixed by Sebastian Heger (#237).
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---
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## Breaking Changes / Compatibility
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- **Minimum Python version raised to 3.10.** Python 3.8 and 3.9 have reached end-of-life and
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are no longer tested or supported.
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- Bundled CBC libraries removed — `cbcbox` is now a required dependency (installed
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automatically via pip).
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- `gurobipy` version constraint relaxed to `>=10` (no upper bound).
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- `cffi` version constraint relaxed to `>=1.15` (no upper bound).
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- `highsbox` version constraint relaxed to `>=1.10.0` (no upper bound).
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---
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## Acknowledgements
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This release was a team effort. Thank you to everyone who contributed:
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- **Robert Schwarz** — HiGHS interface: initial implementation (PR #332) and extensive
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improvements (PR #418), including objective setter fix, option types, test coverage and
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`highsbox` migration. Co-authored with **Bernard Zweers** and **Miguel Hisojo**.
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- **Túlio Toffolo** — macOS Apple Silicon support, HiGHS testing infrastructure, CI
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modernisation, and many quality-of-life fixes.
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- **Sebastian Heger** — Bug fix for constraints with empty linear expressions (#237).
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- **Dominik Peters** — Removed upper limit on supported Python versions (#408).
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- **Adeel Khan** — HiGHS `_core` library support.
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- **Haroldo Santos** — cbcbox integration, CBC bug fixes, CI/CD automation, and release management.

‎RELEASE-ANNOUNCEMENT.md‎

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# python-mip 1.17 Released 🎉
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We are pleased to announce the release of **python-mip 1.17**, the first new release since
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1.15.0. This version brings a new solver backend, major infrastructure improvements, and several
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bug fixes.
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---
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## What's New
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### HiGHS is now a supported solver
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python-mip 1.17 ships with full support for [HiGHS](https://highs.dev) — a high-performance,
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open-source LP/MIP solver with an MIT licence. HiGHS joins CBC and Gurobi as a first-class
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backend. It supports LP and MIP solve, warm-starting for LP re-solves, and the full
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python-mip constraint/variable API.
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To use HiGHS, install the optional dependency:
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```
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pip install mip[highs]
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```
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This work was led primarily by **Robert Schwarz**, with contributions from **Túlio Toffolo**,
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**Adeel Khan**, **Bernard Zweers**, and **Miguel Hisojo**. The integration spanned many months
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of careful incremental work — thank you all!
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### CBC binary distribution: a new era with `cbcbox`
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One of the longest-standing pain points in python-mip has been shipping up-to-date CBC binaries.
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Historically, pre-built `.so`/`.dylib`/`.dll` files lived directly in the python-mip repository,
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which meant updating CBC required a full python-mip release and manually building binaries for
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each platform.
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**With 1.17, we have completely decoupled CBC binary distribution** into a new companion package,
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[cbcbox](https://pypi.org/project/cbcbox/). `cbcbox` ships pre-built CBC wheels for:
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- Linux x86\_64 and aarch64
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- macOS x86\_64 and arm64 (Apple Silicon, native — no Rosetta!)
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- Windows x64
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`cbcbox` is installed automatically as a dependency of python-mip. Future CBC upgrades can now
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be shipped by releasing a new `cbcbox` version — completely independently of python-mip.
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A big thank you to **Túlio Toffolo** for also building the first macOS ARM64 CBC binary for the
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transition period, and for co-developing the `cbcbox` tooling.
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### Automated releases via GitHub Actions
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Starting with this release, publishing a new version of python-mip to PyPI is as simple as
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pushing a version tag:
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```
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git tag v1.17 && git push --tags
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```
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A GitHub Actions workflow using OIDC Trusted Publisher takes care of building and uploading
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to PyPI automatically, with no API tokens to manage.
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### Python 3.10–3.13 + PyPy 3.11 support; minimum raised to 3.10
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python-mip now officially supports Python 3.10, 3.11, 3.12, 3.13 and PyPy 3.11, tested across
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Linux (x86\_64 and arm64), macOS (Apple Silicon), and Windows. Python 3.8 and 3.9 have reached
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end-of-life and are no longer supported.
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---
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## Bug Fixes
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- **CBC re-solve correctness**: Calling `optimize()` multiple times on the same model could
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return stale results due to a behavioural change in newer CBC. Fixed.
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- **Empty `LinExpr` in constraints** handled correctly (thanks **Sebastian Heger**, #237).
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- **Windows DLL loading** fixed for Python 3.8+ (`os.add_dll_directory` now used).
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---
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## Upgrading
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```
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pip install --upgrade mip
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```
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For HiGHS support:
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```
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pip install --upgrade "mip[highs]"
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```
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---
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## Contributors
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Thank you to everyone who contributed code, bug reports, and reviews since 1.15:
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**Robert Schwarz** · **Túlio Toffolo** · **Sebastian Heger** · **Dominik Peters** ·
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**Adeel Khan** · **Bernard Zweers** · **Miguel Hisojo** · **Haroldo Santos**
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---
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Full changelog: https://github.com/coin-or/python-mip/blob/master/CHANGELOG.md
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PyPI: https://pypi.org/project/mip/1.17/

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