I'd like to, but it only sets the tracing to the currently running thread (the request is for setting the tracing for other threads).

Just for info, the problem I'm solving is that the debugger is multi-threaded, but the user can start the code without any tracing in place, and then, when it gets to an attach to process or a programmatic attach to the debugger, the debugger needs to set the tracing to threads that are already running (and any new thread created afterward) and Python doesn't really have any structure for that in place (so, I'm using the C-API as a workaround to do what PyEval_SetTrace does but targeting any thread).