This is different case than mutating a dict while iterate it. In this case the failure is caused by GC, and it is always hard to handle such issues. In case of a dict you can just copy it before iterating. But what to do with RuntimeError from slicing a list if copying a list is vulnerable to the same issue?

The example of yet one solution you can see in dict_keys() in dictobject.c. I always wondered why this code is needed.