🐛 fix(venv): resolve Python spec from env name when tox passes fallback path#308
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gaborbernat merged 1 commit intotox-dev:mainfrom Mar 10, 2026
Merged
🐛 fix(venv): resolve Python spec from env name when tox passes fallback path#308gaborbernat merged 1 commit intotox-dev:mainfrom
gaborbernat merged 1 commit intotox-dev:mainfrom
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Tox 4.47.1+ extracts base_python from version factors in env names (PR #3846). When the requested Python doesn't exist (e.g. 9.99), tox passes a fallback interpreter path to _get_python(). The old code used this fallback path's Python info, losing the original version spec. This caused test_uv_venv_spec_full_implementation to fail because uv was invoked with the fallback Python version instead of the requested 9.99. The fix: when _get_python() receives an absolute path, parse the env name (self.name) as a PythonSpec first. If it contains version info, use that spec. Otherwise fall back to probing the absolute path. This preserves the user's intent from the env name while handling cases like 'demo' that have no version info. Also simplified env_version_spec() by removing the executable and sys.executable shortcircuits that are no longer needed with this approach.
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Tox 4.47.1 changed how
base_pythonis extracted from environment names (PR #3846). When parsing multi-factor env names like3.10-tests, it now checks each factor against version patterns. 🔍 If the requested Python doesn't exist, tox passes a fallback interpreter's absolute path to_get_python()instead of a version spec.The previous code used this fallback path directly in
env_version_spec(), losing the original version specification from the environment name. When tests requested Python 9.99 to validate spec generation, uv received/usr/bin/python3.14instead ofcpython9.99, causing failures.The fix separates version-aware environments from generic ones. When
_get_python()receives an absolute path, it parses the environment name (self.name) as aPythonSpec. ✨ If the name contains version info, that spec is used. If not (like env namepy), the absolute path is probed and stored inPythonInfo.extra["executable"]for environments that need a specific interpreter.This preserves the user's intent from the environment name while handling both lock runner workflows (which need absolute paths for generic envs) and regular workflows (which need version specs for versioned envs).