method names in __slots__ ??

[John Machin]

I have stumbled across some class definitions which include all/most
method names in a __slots__ "declaration". A cut-down and disguised
example appears at the end of this posting.

Never mind the __private_variables and the getter/setter approach, look
at the list of methods in the __slots__.

I note that all methods in an instance of a slotted class are read-only
irrespective of whether their names are included in __slots__ or not:
Given a = Adder(),
    a.tally = 0
gets AttributeError: 'Adder' object attribute 'tally' is read-only
    a.notinslots = 1
gets AttributeError: 'Adder' object attribute 'notinslots' is read-only

So is there some magic class-fu going down here, or is this just a
waste of memory space in the instances?

=== example ===
# class with method names in __slots__

class Adder(object):

    __slots__ = [
        # methods
        '__init_',
        'get_foo',
        'get_value',
        'set_foo',
        'tally',
        # private variables
        '__foo',
        '__value',
        # public variables
        'bar',
        'zot',
        ]

    def __init__(self, start=0):
        self.__value = start
        self.__foo = 666
        self.bar = None
        self.zot = 42

    def tally(self, amount):
        self.__value += amount

    def get_value(self):
        return self.__value

    def set_foo(self, arg):
        self.__foo = arg

    def get_foo(self):
        return self.__foo
        
    def notinslots(self):
        pass
=== end of example ===