> Okay. The test verifies work done to minimize interpreter startup time, but probably the relative cost of importing functools (and thus collections et al) isn't significant compared to the overall cost of spawning a process in a Windows desktop environment. That may not be the case for Nano Server and IoT Core.

Is there an easy way to measure this?

> PYTHONIOENCODING=cp65001

I tried setting PYTHONIOENCODING=cp1252 on Windows IoT Core as a workaround and it didn't work.

Victor> My PR 13110 avoids "import functools" at startup. Can you please try it and check if it fix test_site?

I tried the PR and it fixes test_startup_imports, which seems promising.  The PR breaks other test_site tests on Windows IoT Core. 
 The same ones you pointed out in the PR discussion.