bpo-39717: Fix exception causes in tarfile module

[cool-RR]

https://bugs.python.org/issue39717

[codecov]

Codecov Report

Merging #18595 into master will increase coverage by 1.01%.
The diff coverage is n/a.

@@ Coverage Diff @@ ## master #18595 +/- ## =========================================== + Coverage 82.11% 83.13% +1.01%  =========================================== Files 1956 1571 -385 Lines 589413 414817 -174596 Branches 44458 44458 =========================================== - Hits 484015 344856 -139159  + Misses 95748 60335 -35413  + Partials 9650 9626 -24 

Impacted Files	Coverage Δ
Lib/distutils/tests/test_bdist_rpm.py	30.00% <0.00%> (-65.00%)	⬇️
Lib/distutils/command/bdist_rpm.py	7.63% <0.00%> (-56.88%)	⬇️
Lib/test/test_urllib2net.py	76.92% <0.00%> (-13.85%)	⬇️
Lib/test/test_smtpnet.py	78.57% <0.00%> (-7.15%)	⬇️
Lib/ftplib.py	63.85% <0.00%> (-6.06%)	⬇️
Lib/test/test_ftplib.py	87.11% <0.00%> (-4.72%)	⬇️
Tools/scripts/db2pickle.py	17.82% <0.00%> (-3.97%)	⬇️
Tools/scripts/pickle2db.py	16.98% <0.00%> (-3.78%)	⬇️
Lib/test/test_socket.py	71.94% <0.00%> (-3.77%)	⬇️
Lib/test/test_asyncio/test_base_events.py	91.84% <0.00%> (-3.30%)	⬇️
... and 430 more

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[cool-RR]

Is the codecov failure a real thing that I need to deal with? Because it's showing coverage changes for totally different files and I don't understand how that's related to my change.

[ethanfurman]

Most of these should be either from None or raise BlahError('some message [%s]' % str(e)) from None.

Do we know of any cases where including the previous exception adds value instead of noise?

[ethanfurman]

@cool-RR: I'm not sure what's up with code coverage either. Ignore it.