A module is a singleton. No matter how many times you import foo, the namespace foo is always the same. If you reassign foo.bar in in code in module x, then later access foo.bar from module y, it will be the value assigned in X.

This is not amenable to inheritance tho, however there is a strong argument against inheritance in singletons anyway. Further, the borg pattern is considered "more pythonic" in the case of inheritable singletons, as frequently what is desired in such cases is shared state vs instead of shared identity.