[issue25872] multithreading traceback KeyError when modifying file

[Roundup Robot]

Change by Roundup Robot <devnull at psf.upfronthosting.co.za>:


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pull_requests: +16845
pull_request: https://github.com/python/cpython/pull/17360

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue25872>
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