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GeezerVison is showing github.com — gh-155944: Catch only expected errors in getDOMImplementation fallback by tobiaspal · Pull Request #155948 · python/cpython

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@tobiaspal

@tobiaspal tobiaspal commented Aug 17, 2026 •
edited by bedevere-app Bot
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Don't catch all exceptions from the well_known_implementations candidates, because only the expected ImportError and AttributeError mean the implementation is unavailable.

Found via @devdanzin's AI-assisted audit of Lib/; working on it at the PyCon Korea 2026 sprint.

In well_known_implementations the xml.dom.DOMImplementation seems to be a leftover from PyXML, so only xml.dom.minidom is used (comes from Lib/xml/dom/minidom.py):

cpython/Lib/xml/dom/domreg.py

Lines 11 to 14 in b6c11fe

well_known_implementations = {
'minidom':'xml.dom.minidom',
'4DOM': 'xml.dom.DOMImplementation',
}

Claude Code helped write the tests and the fix.

  • Issue: xml.dom.domreg.getDOMImplementation: fallback discovery masks genuine bugs, not just "not installed" #155944

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@tobiaspal
pythongh-155944: Catch only expected errors in getDOMImplementation f…
f806830 
…allback

Don't catch all exceptions from the `well_known_implementations` candidates, because only the expected `ImportError` and `AttributeError` mean the implementation is unavailable.
@bedevere-app bedevere-app Bot mentioned this pull request Aug 17, 2026
xml.dom.domreg.getDOMImplementation: fallback discovery masks genuine bugs, not just "not installed" #155944
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@bedevere-app bedevere-app Bot added the awaiting review label Aug 17, 2026
@picnixz picnixz closed this Aug 17, 2026
@picnixz

picnixz commented Aug 17, 2026

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See #155944 (comment) for rationale of closing.
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@tobiaspal @picnixz
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