What is the difference between SimpleNamespace and empty class definition?

This is explained pretty well in the types module description. It shows you that types.SimpleNamespace is roughly equivalent to this:

class SimpleNamespace:
    def __init__(self, **kwargs):
        self.__dict__.update(kwargs)

    def __repr__(self):
        keys = sorted(self.__dict__)
        items = ("{}={!r}".format(k, self.__dict__[k]) for k in keys)
        return "{}({})".format(type(self).__name__, ", ".join(items))

    def __eq__(self, other):
        return self.__dict__ == other.__dict__

This provides the following advantages over an empty class:

1. It allows you to initialize attributes while constructing the object: sn = SimpleNamespace(a=1, b=2)
2. It provides a readable repr(): eval(repr(sn)) == sn
3. It overrides the default comparison. Instead of comparing by id(), it compares attribute values instead.