✨ feat(config): add default_base_python config key#3783
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gaborbernat merged 1 commit intotox-dev:mainfrom Feb 20, 2026
Merged
✨ feat(config): add default_base_python config key#3783gaborbernat merged 1 commit intotox-dev:mainfrom
gaborbernat merged 1 commit intotox-dev:mainfrom
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Environments without a Python factor or explicit base_python now consult default_base_python before falling back to sys.executable. This lets projects pin a fallback interpreter for reproducibility without conflicting with pyXY factor-named environments.
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Environments without a Python factor in their name (e.g.
lint,type,docs) currently fall back tosys.executablewhenbase_pythonisn't explicitly set. This means the interpreter varies across machines — Ubuntu 22.04 defaults to 3.10, Fedora 37 to 3.11 — harming reproducibility and causing unexpected failures when dependencies don't support the host's Python version. 🔧 Settingbase_pythonglobally in[env_run_base]works around this but conflicts withpyXYfactor-named environments.The new
default_base_pythonkey sits at the environment config level and acts as a fallback only when no Python factor is detected and no explicitbase_pythonis set. This gives it clear precedence semantics: Python factor > explicitbase_python>default_base_python>sys.executable. Placing it in[env_run_base]rather than[tox]allows per-environment overrides when needed.✨ Existing configurations are unaffected since the default remains
sys.executable. This closes #2846.