[issue39717] Fix exception causes in tarfile module

[Raymond Hettinger]

New submission from Raymond Hettinger <raymond.hettinger at gmail.com>:

What do you think it is necessary to switch from implicit chaining to explicit chaining?

If anyone is currently relying on __context__ vs __cause__, this patch will break their code.

In a traceback, the only visible difference is in the text between the exceptions:

- During handling of the above exception, another exception occurred:
+ The above exception was the direct cause of the following exception:

While we haven't been 100% consistent about this, the norm has been to either use implicit chaining or use "from None" to turn-off chaining.  The "from e" approach can be used to alter the explicit chain, perhaps skipping over one or more exceptions, but that isn't the case here.

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nosy: +rhettinger

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue39717>
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