From the release announcement: "This is a special bugfix release ahead of
schedule to address a memory leak that was happening on certain function calls
when using Cython. The memory leak consisted of a small constant amount of bytes
in certain function calls from Cython code. Although in most cases this was not
very noticeable, it was very impactful for long-running applications and certain
usage patterns. Check bpo-46347 for more information."
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