[issue40700] Make WSGIRequestHandler easier to be customized by the user

[Manjusaka]

Change by Manjusaka <lizheao940510 at gmail.com>:


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keywords: +patch
pull_requests: +19548
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/20262

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40700>
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