How can I find all classes with no mixins?

I am currently using brute force with the schema view:

```Python
all_classes = schema.all_classes()
all_classes = list(all_classes.keys())

mixers = []
for i in all_classes:
    print(i)
    checkee = all_classes.get_class(i)
    mixers = mixers + checkee.mixins

mixers = list(set(mixers))

unmixed = list(set(all_classes) - set(mixers))
```