> The reference leak was introduced in 86ea58149c3 / GH-13159 / bpo-36737. PR GH-20929 fixes it, too.
Usually, it's not that the subinterpreter work introduces new leak, but makes old leak suddenly visible.
The create_filter() leak was introduced way earlier:
commit 9b99747386b690007027c3be2a5d7cfe3d3634f5
Author: Nick Coghlan <ncoghlan@gmail.com>
Date: Mon Jan 8 12:45:02 2018 +1000
bpo-31975 (PEP 565): Show DeprecationWarning in __main__ (GH-4458)
It's a minor leak since the create_filter() function is called exactly 5 times at startup. It's a leak of 5 strong references, it's not a big deal :-)