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'