During interpreter shutdown, depending on the order in which things happen, a module can be unloaded before all instances of classes defined in that module are garbage collected.
In particular, this means that any global variables (including imported modules) become `None` by the time the instances `__del__` is called, resulting in
```
AttributeError: 'NoneType' object has no attribute 'wc_FreeRng'
```
being displayed while the process exits. This can be avoided simply by catching and ignoring the `AttributeError` in this case, since the process is shutting down anyways.
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