design question: no new attributes

[Ben Finney]

"Alan Isaac" <aisaac at american.edu> writes:

> OK, let me approach this from a new direction.  Suppose I define a
> class that behaves I think as I stipulated::
>
> class NothingNew:
>     a = 0
>     def __init__(self):
>         self.b = 1
>         self.initialized = True
>     def __setattr__(self, attr, val):
>         if not hasattr(self,'initialized') or hasattr(self, attr):
>             self.__dict__[attr] = val
>         else:
>             raise ValueError
>
> After adding some documentation, what are the downsides?

The biggest downside I see is that you're going through contortions to
solve a problem you haven't demonstrated actually exists.

A smaller problem is that the ValueError should describe what's going wrong:

    raise ValueError("The author of this class thinks you're up to no good")

Really, though, adding attributes to an instance is a normal thing to
do in Python, and you've not yet shown why you want that normal
functionality to be special-cased here.

-- 
 \             "Experience is that marvelous thing that enables you to |
  `\      recognize a mistake when you make it again."  -- Franklin P. |
_o__)                                                            Jones |
Ben Finney