You have — essentially — no use for __slots__.
For the time when you think you might need __slots__, you actually want to use Lightweight or Flyweight design patterns. These are cases when you no longer want to use purely Python objects. Instead, you want a Python object-like wrapper around an array, struct, or numpy array.
class Flyweight(object):
def get(self, theData, index):
return theData[index]
def set(self, theData, index, value):
theData[index]= value
The class-like wrapper has no attributes — it just provides methods that act on the underlying data. The methods can be reduced to class methods. Indeed, it could be reduced to just functions operating on the underlying array of data.