pybind/pybind11 v3.1.0

Version 3.1.0

on GitHub

New Features:

• Support for Python 3.8 was removed. The minimum supported version is now Python 3.9. #6110

• Support for MSVC 2017 has been dropped. #6110

• Changed strict-mode numeric conversions for PEP 484 compatibility: float now accepts int, and complex now accepts int and float. #5879

• Small extra features added to the pybind11 command line tool based on python-config. #4272

• Added subinterpreter_thread_state, an RAII wrapper that owns a reusable PyThreadState for a sub-interpreter, together with a subinterpreter_scoped_activate overload that activates it. This lets an OS thread re-enter one or more sub-interpreters without creating and destroying a PyThreadState on every activation. #6073

• Add py::mod_gil_used() as replacement spelling to py::mod_gil_not_used(false). #5797

Bug fixes:

• Fixed a crash in py::subinterpreter::create() when called without a current PyThreadState, which its documentation explicitly allows — for example from an embedder that ended initialization with PyEval_SaveThread(), or from a worker thread that has never touched Python. error_scope is now constructed after a thread state has been attached instead of before. #6127

• Make py::print delegate to the current frame/interpreter built-ins print entry, fixing handling of sys.stdout = None, following the active runtime's stream, keyword, and error semantics, and remaining a no-op if the entry is unavailable during teardown. #6121

• Include the builtin complex type in the input annotation of the std::complex<T> type caster. #6113

• String views (e.g. std::string_view) are now kept alive only when loaded from a transient source (such as a generator), fixing both a use-after-free and a regression where casting a view from a durable object outside a bound function would throw. #6096

• Drop Python 2 prepend to evaluated source, causing errors to be off by one. #6089

• Fix data race on last_storage_ptr_ cache in gil_safe_call_once_and_store. #6087

• Allow user defined __str__ on enum_. #6078

• Fix generated Callable type annotations for Python callbacks passed into C++ by inverting the callback's argument/return I/O context relative to the enclosing function signature. #6055

• Correct __delitem__ for negative-step slices and re-enable contiguous erase fast path. #6088

• Do not pass -fno-fat-lto-objects to GCC on macOS, which made all LTO probes fail and silently disabled LTO. #6114

• Fixed cross-compilation to Emscripten/Pyodide with CMake ≥ 4.1 by no longer overriding an explicitly set PYBIND11_USE_CROSSCOMPILING when CMAKE_CROSSCOMPILING_EMULATOR is defined. #6094

• Unset stale PYTHON_MODULE_DEBUG_POSTFIX and correct USE_PYTHON_INCLUDE_DIR variable. #6086

• Apply -undefined dynamic_lookup to all Apple platforms. #6075

Internal:

• Improved py::enum_ operator performance by restoring type-specific implementations. #5887

• Optimized internal std::unordered_map/std::unordered_set hashing paths with noexcept. #5960

CI:

• Test Python 3.15 in CI. #6107

• Updated the CIBW test workflow to cibuildwheel v4.1 and bumped the Pyodide build to 314. #6095