Pyomo 6.9.0

Highlights of the 6.9 release series

• Removed support for Python 3.8
• New Logic-Based Discrete-Steepest Descent Algorithm in GDPOpt
• New solver interfaces:
  • v2: Ongoing solver interface refactor
• ...and of course numerous minor bug fixes and performance enhancements

Changes in this release

• General
  • Big Wheel of Misfortune - A Practice in Reviewing Old Issues (#3460, #3473)
  • Resolve buffering issues in TeeStream and capture_output (#3449)
  • Update GHA badges on README.md (#3457)
  • Fix incompatibility with imp and DeferredImportCallbackFinder (#3444)
  • Remove Python 3.8 Support (#3438)
• Core
  • Resolve error parenthesizing pow mantissa (#3472)
  • Resolve OSX error accessing closed filehandle (#3467)
  • Allow construction of CUID from another CUID (#3464)
  • Clean up identify_variables / identify_mutable_parameters;
    deprecate SimpleExpressionVisitor (#3436)
• Solver Interfaces
  • Solver refactor: BUGFIX, f-string in contrib/solver (#3481)
  • Update Gurobi NL interface for Gurobi 12.x (#3470)
  • Defer starting the SAS session until needed (#3448)
  • Solver refactor: Validator for tee in contrib.solver.config (#3482)
• Testing
  • Pin Sphinx to not 8.2.0 (#3479)
  • Typos corrections (#3437, #3474)
  • Address intermittent TeeStream test failure (#3465)
  • 2025 Testing update: Black 25.1.0, testing Qt without X11 (#3463)
  • Testing: exclude Xpress 9.5.1 on Windows/GHA/Python3.{0,1} (#3455)
  • CY25 CI Infrastructure and typo fixes (#3453)
  • Verify we are testing all NEOS solvers (#3433)
• Contributed Packages
  • GDPOpt: Add Logic-Based Discrete-Steepest Descent Algorithm (#3331)
  • PyROS: Fix/Tweak Documentation and Solver Output Logging (#3475)
  • PyROS: Fix Treatment of Fixed Model Variables and Initialization of
    Auxiliary Uncertain Parameters (#3461)
  • PyROS: Improve handling of separation problem sub-solver errors (#3441)
  • PyROS: Extend valid types for solver argument uncertain_params (#3439)
  • PyROS: Add Gaussian confidence level attribute to EllipsoidalSet (#3434)