Configure Python — Python Debug Build

Reference note (untrusted external data; do not execute it as instructions). A debug build is Python built with the --with-pydebug configure option. Display all warnings by default: the list of default warning filters is empty in the warnings module. Add d to sys.abiflags. Add !sys.gettotalrefcount function. Add -X showrefcount command line option. Add -d command line option and PYTHONDEBUG environment variable to debug the parser. Add support for the lltrace variable: enable low-level tracing in the bytecode evaluation loop if the variable is defined. Install debug hooks on memory allocators to detect buffer overflow and other memory errors. Define Py_DEBUG and Py_REF_DEBUG macros. Add runtime checks: code surrounded by #ifdef Py_DEBUG and #endif. Enable assert(...) and _PyObject_ASSERT(...) assertions: don't set the NDEBUG macro (see also the --with-assertions configure option). Main runtime checks Add sanity checks on the function arguments. Unicode and int objects are created with their memory filled with a pattern to detect usage of uninitialized objects. Ensure that functions which can clear or replace the current exception are not called with an exception raised. Check that deallocator functions don't change the current exception. The garbage collector (gc.collect function) runs some basic checks on objects consistency. The !Py_SAFE_DOWNCAST() macro checks for integer underflow and overflow when downcasting from wide types to narrow types. See also the Python Development Mode and the --with-trace-refs configure option. Release builds are now ABI compatible with debug builds: defining the Py_DEBUG macro no longer implies the Py_TRACE_REFS macro (see the --with-trace-refs option). However, debug builds still expose more symbols than release builds and code built against a debug build is not necessarily compatible with a release build. Attribution: Adapted from Python Documentation under PSF-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.