__slots__ is meaningless.

It is meaningless to use ```__slots__``` in ```__init__```. Python creates ```__dict__``` and ```__weakref__```  before ```__init__``` invocation.

See:
```python
   >>> class A(object):
   ...   def __init__(self):
   ...     self.a = 5
   ... 
   >>> a = A() 
   >>> dir(a)
  ['__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'a']
   >>> class B(object):
   ...   def __init__(self):
   ...     self.__slots__ = "a"
   ...     self.a = 5
   ... 
   >>> b = B()
   >>> dir(b)
   ['__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__slots__', '__str__', '__subclasshook__', '__weakref__', 'a']
   >>> class C(object):
   ...   __slots__ = "a"
   ...   def __init__(self):
   ...     self.a = 5
   ... 
   >>> c = C()
   >>> dir(c)
   ['__class__', '__delattr__', '__doc__', '__format__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__slots__', '__str__', '__subclasshook__', 'a']
   >>> 
```