> The main question is if anyone ever used Py_TRACE_REFS? Does someone
> use sys.getobjects() or PYTHONDUMPREFS environment variable?

I used sys.getobjects() today to track down a memory leak in the mypyc-compiled version of mypy.

We were leaking memory badly but no sign of the leak was showing up in mypy's gc.get_objects() based profiler. Using a debug build and switching to sys.getobjects() showed that we were badly leaking int objects. A quick inspection of the values in question (large and random looking) suggested we were leaking hash values, and that quickly pointed me to https://github.com/mypyc/mypyc/pull/562.

I don't have any strong feelings about whether to keep it in the "default" debug build, though. I was using a debug build that I built myself with every debug feature that seemed potentially useful.