repoview: separate concerns in _filteredrepotypes comment The cited issue in Python bugtracker is closed, but hasn't been fixed. We've been able to use the attached example and reproduce it with Python 3.9. The point where it turns from needless stress on the GC to the an actual leak is when one factors in the fact that the GC was before Python 3.4 unable to collect some types (see PEP 442). Note that even with Python 2.7, the simple example of cycles due to __mro__ are collectable. This was seen again with the example attached on the CPython issue.