[Python-Dev] Re: closure semantics

Fri Oct 24 17:10:03 EDT 2003

At 01:39 PM 10/24/03 -0700, Zack Weinberg wrote:
>class foo:
> A = 1 # these are class variables
> B = 2
> C = 3
>> def __init__(self):
> self.a = 4 # these are instance variables
> self.b = 5
> self.c = 6
>>I find this imperative syntax for declaring instance variables
>profoundly unintuitive. Further, on my first exposure to Python, I
>thought A, B, C were instance variables, although it wasn't hard to
>understand why they aren't.

A, B, and C *are* instance variables. Why do you think they aren't?
>People like to rag on the popularity of __slots__ (for reasons which
>are never clearly spelled out, but never mind) -- has anyone
>considered that it's popular because it's a way of declaring the set
>of instance variables,

What good does declaring the set of instance variables *do*? This seems to 
be more of a mental comfort thing than anything else. I've spent most of 
my career in declaration-free languages, though, so I really don't 
understand why people get so emotional about being able to declare their 
variables.
> and there is no other way in the language?

Actually, there are a great many ways to implement such a thing. One way 
might be something like:
class RestrictedVars:
 vars = ()
 def __setattr__(self,attr,name):
 if name not in self.vars:
 raise AttributeError("No such attribute",attr)
class SomeClass(RestrictedVars):
 vars = 'a','b','c'