python.wut

>>> class Wut(object):
...   __slots__ = ('a',)
...
>>> Wut()
<__main__.Wut object at 0x7ffff7f55b40>
>>> Wut().b = 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'Wut' object has no attribute 'b'

>>> class Eva(Wut): pass
...
>>> Eva().b = 1
>>> Eva()
<__main__.Eva object at 0x7ffff1be8098>
>>> vars(Eva())
{}