Fix unhelpful KeyError when using invalid VIRTUALENV_DISCOVERY value#3031
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gaborbernat merged 3 commits intopypa:mainfrom Feb 15, 2026
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When an invalid discovery method is specified via the VIRTUALENV_DISCOVERY environment variable, virtualenv now raises a clear ValueError listing all available discovery methods instead of showing a confusing KeyError. This improves the user experience by making it immediately clear what went wrong and what the valid options are, especially useful when the error appears in the middle of a long tox stacktrace. Fixes pypa#2896
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gaborbernat
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veeceey
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The test_invalid_discovery_method_via_env test was expecting a ValueError with the old error format from PR pypa#3031, but our changes raise a RuntimeError with improved messaging. Update the test assertions to match. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
veeceey
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Feb 16, 2026
The test_invalid_discovery_method_via_env test was expecting a ValueError with the old error format from PR pypa#3031, but our changes raise a RuntimeError with improved messaging. Update the test assertions to match. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Fixes #2896
Problem
When an invalid discovery method is specified via the
VIRTUALENV_DISCOVERYenvironment variable, virtualenv shows an unhelpfulKeyErrorinstead of a clear error message. This is especially confusing when the error appears buried in tox stacktraces.Before:
After:
Changes
get_discover()to check if the specified discovery method exists before attempting to access itValueErrorwith a helpful message listing all available discovery methodsTesting
Manually tested with:
Both now show clear error messages instead of KeyError. All existing tests pass.