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python-mip 1.17.1 Released 🎉

We are pleased to announce the release of python-mip 1.17.1, the first publicly available release in quite some time. This is a patch release on top of 1.17, which itself brought a new solver backend, major infrastructure improvements, and several bug fixes. 1.17.1 delivers important stability fixes for CBC and updated binaries via cbcbox 2.910.

What's New in 1.17.1

CBC crash fix: Gomory Mixed-Integer cuts (CutType.GMI)

A crash was discovered when using CutType.GMI with recent CBC versions. The root cause was a bug in scaleCutIntegral — a function shared by OsiCuts and CglGomory — that modified coefficient arrays in place before asserting integrality, causing an abort() when borderline floating-point rounding left a value just outside the 1e-9 tolerance. The fix (pre-check all values before applying any modification) was committed directly to the upstream COIN-OR repositories coin-or/Osi and coin-or/Cgl and is included in cbcbox 2.910.

Updated CBC binaries via cbcbox 2.910

python-mip 1.17.1 requires cbcbox>=2.910, which ships binaries built from the latest COIN-OR master (post-fix). The new wheels include:

  • The scaleCutIntegral crash fix in both Osi and Cgl
  • Updated CutType C enum (CT_LaGomory removed; entries renumbered) correctly reflected in python-mip's ffi.cdef
  • Performance improvements from recent COIN-OR master commits

cbcbox: faster CBC, simpler releases

cbcbox is now the sole distribution channel for CBC binaries. This decoupling means future CBC improvements — algorithm enhancements, bug fixes, new COIN-OR master commits — can reach users with a cbcbox release alone, without touching python-mip at all. The release cycle for CBC upgrades is now:

  1. Push fix to upstream COIN-OR (coin-or/Cbc, coin-or/Cgl, coin-or/Osi, …)
  2. Bump cbcbox version and push — CI builds all platforms automatically
  3. Bump cbcbox>=X.Y in python-mip pyproject.toml and push a tag

On x86_64 (Linux, macOS, Windows), cbcbox ships two complete solver stacks per wheel:

Variant OpenBLAS kernel Description
generic DYNAMIC_ARCH runtime dispatch Compatible with any x86_64 CPU
avx2 HASWELL 256-bit AVX2/FMA Optimised for Haswell (2013+) and newer

The best variant is selected automatically at import time. The AVX2 build delivers measurable speedups on modern hardware thanks to wider SIMD in the dense linear algebra kernels used by Clp's simplex solver.

What's New in 1.17 (first release since 1.15.0)

HiGHS is now a supported solver

python-mip 1.17 ships with full support for HiGHS — a high-performance, open-source LP/MIP solver with an MIT licence. HiGHS joins CBC and Gurobi as a first-class backend. It supports LP and MIP solve, warm-starting for LP re-solves, and the full python-mip constraint/variable API.

HiGHS binaries are distributed via highsbox, installed automatically as an optional dependency:

pip install mip[highs]

This work was led primarily by Robert Schwarz, with contributions from Túlio Toffolo, Adeel Khan, Bernard Zweers, and Miguel Hisojo. The integration spanned many months of careful incremental work — thank you all!

CBC binary distribution via cbcbox

Historically, pre-built CBC binaries lived directly in the python-mip repository, requiring a full python-mip release for every CBC update and manual cross-platform builds.

With 1.17, CBC binary distribution is fully decoupled into cbcbox, a dedicated companion package with pre-built wheels for:

  • Linux x86_64 and aarch64
  • macOS x86_64 and arm64 (Apple Silicon, native — no Rosetta!)
  • Windows x64

cbcbox is installed automatically. The same architecture applies to HiGHS via highsbox.

Automated releases via GitHub Actions

Publishing a new version of python-mip to PyPI is now as simple as:

git tag v1.17.1 && git push --tags

A GitHub Actions workflow using OIDC Trusted Publisher handles building and uploading to PyPI with no API tokens to manage.

Python 3.10–3.13 + PyPy 3.11; minimum raised to 3.10

python-mip now officially supports Python 3.10, 3.11, 3.12, 3.13 and PyPy 3.11, tested across Linux (x86_64 and arm64), macOS (Apple Silicon), and Windows. Python 3.8 and 3.9 have reached end-of-life and are no longer supported.

Bug Fixes (cumulative 1.17 + 1.17.1)

  • GMI cut crash (CutType.GMI): scaleCutIntegral assert in Osi/Cgl. Fixed upstream.
  • CBC re-solve correctness: optimize() called multiple times could return stale results. Fixed by calling Cbc_reset() before each solve.
  • Empty LinExpr in constraints handled correctly (thanks Sebastian Heger, #237).
  • Windows DLL loading fixed for Python 3.8+ (os.add_dll_directory now used).
  • Stale HiGHS error message corrected to reference highsbox instead of highspy.

Upgrading

pip install --upgrade mip

For HiGHS support:

pip install --upgrade "mip[highs]"

Contributors

Thank you to everyone who contributed code, bug reports, and reviews since 1.15:

Robert Schwarz · Túlio Toffolo · Sebastian Heger · Dominik Peters · Adeel Khan · Bernard Zweers · Miguel Hisojo · Haroldo Santos

Full changelog: https://github.com/coin-or/python-mip/blob/master/CHANGELOG.md

PyPI: https://pypi.org/project/mip/1.17.1/