__slots__ query

[Gustavo Cordova]

> 
> I notice that in 2.2 it's possible to do strange things to slots via
> instances.
> 

Strange to you, but pretty obvious to me:

1. You define a class with a specification of allowing
   for two (only two) attribute slots, named "a" and "b":

> Thus 
> >>> class A(object):
> ...     __slots__ = ['a','b']
> ... 

2. You instantiate such a class.
   Note: The object you used to define which slots you
   wanted was mutable, but after defining the class,
   __slots__ may no longer be needed.

> >>> a=A()
> >>> a.c=2
> ===> error
> >>> a.__slots__.append('c')
> >>> a.c=2
> ===> error
> >>> a.__slots__
> ['a', 'b', 'c']
> >>> A.__slots__
> ['a', 'b', 'c']
> >>> b=A()
> >>> b.c=2
> ===> error

Seems pretty natural to me. I'd be alarmed if there
actually *was* a .c attribute.

The __slots__ object might be mutable, it doesn't
mean that you can add attributes anytime after
defining the class.


-gustavo