Comment by murderfs

> Is Python's GC bad, or are there cyclic reference issues?

Unless you're being pedantic and including reference counting without cycle detection as GC, if your GC has cyclic reference issues, your GC is bad.

> Is it possible to detect cyclic references perfectly?

Yes? That's the entire point of tracing GC. You have some set of root objects that you start with (globals, objects on thread stacks, etc.) and then you mark every object that's reachable from them. Anything that's not reachable is garbage, even if there are cycles within them.