🐛 fix(spec): discover debug (Py_DEBUG) interpreters like python3.13-dbg#96
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python3.13-dbg parsed as version 3.13 with machine="dbg", so a real Py_DEBUG interpreter was rejected during discovery. Recognize d, -dbg and -debug as a debug-build marker instead, matching against PythonInfo.debug_build. Absent a marker the build type stays unconstrained, so release specs behave as before. Fixes tox-dev/tox#3977.
gaborbernat
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Debian, Fedora and upstream all install the abiflags-suffixed debug binary (pythonX.Yd, pythonX.Ytd), but _find_possible_exe_names only generated the Windows (_d) and Debian (-dbg) forms, so venv-to-system resolution missed it. Add the d suffix. Sync the spec-format docs across all Diataxis sections: add the debug node to both grammar diagrams, document the t-before-d and arch-before- machine ordering, list debug_build in the metadata reference, and add a how-to for selecting a debug build.
discover_exe matched a base interpreter by name, version, implementation and architecture, but not by its ABI flags. A debug or free-threaded virtualenv could therefore resolve to a release build of the same version. Compare free_threaded and debug_build too, so the runtime value confirms the name-level match.
gaborbernat
approved these changes
Jul 8, 2026
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Debian and Ubuntu ship their
Py_DEBUGinterpreter aspython3.13-dbg, but that spec failed to resolve. 🐛 The parser read the-dbgsuffix as a machine (ISA) nameddbg, and because the real binary reports its true architecture (arm64,x86_64, and so on), no interpreter matched. This surfaced in tox-dev/tox#3977, wherebase_python = python3.13-dbgfell over with "could not find python interpreter".The spec grammar now carries a debug flag next to the free-threaded
tflag. ✨ It accepts the ABI-flag formpython3.13dand Debian'spython3.13-dbg/python3.13-debug, then matches that flag against the interpreter'sPy_DEBUGbuild setting during discovery. A lookahead anchors the marker so it leaves the ISA intact:cpython3.12-64-arm64still readsarm64as the machine. The generated filename pattern and the by-name executable search gained the same forms, so a Debian-dbgbinary also resolves through the venv-to-system walk.The flag defaults to unconstrained. A versioned spec with no marker keeps matching either build type, so no existing spec shifts meaning; only an explicit
d/-dbg/-debugnarrows the search to a debug interpreter.