[issue17188] Document 'from None' in raise statement doc.

[Terry J. Reedy]

Terry J. Reedy added the comment:

The double listing seems to be a glitch.

Either someone else does backport or online doc change waits until I can do it.

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assignee: docs at python -> terry.reedy
stage: patch review -> backport needed
versions: +Python 3.6, Python 3.7 -Python 3.4, Python 3.5

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue17188>
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