ExceptionGroup for TarFile.extractall

encukou · April 18, 2023, 1:44pm

Error handling for TarFile.extractall currently allows relatively little control over individual issues. Using errorlevel you can ignore “fatal” or “non-fatal” errors, and using debug you can optionally log ignored ones to sys.stderr. If an error is not ignored, it is raised, which aborts the extraction. So, you can’t extract as much as possible and get structured information about what failed.

This sounds like a good use case for exception groups.
My idea for an API:

errorlevel=3 turns on exception group reporting: all Exception errors from extracting individual members are collected, and (if any are found) raised in an ExceptionGroup when the extraction finishes.
ExtractError gains a member attribute, which contains the TarInfo object for the failed entry
All other exceptions are “wrapped” in ExtractError, so that this member is always accessible: ExtractError gains a exception attribute, which contains the exception. In some current cases where ExtractError is raised, we’ll need to create an appropriate exception to put here.

If you (yes you!) want to add this to Python 3.13, I can help.

The alternative to wrapping everything in ExtractError is to subclass ExceptionGroup to expose the member <-> error relation in another way. This was discussed in bpo-90589 and discussions leading up to it. But I think wrapping is easier.