automatic accessors to a member var dict elements?

[Bengt Richter]

On Thu, 14 Oct 2004 17:56:09 -0700, Jeff Shannon <jeff at ccvcorp.com> wrote:
[...]
>
>If you really do need to maintain the dict separately, then you can use 
>__getattr__() and __setattr__() to redirect accesses of nonexistent 
>attributes into operations on your contained dict, something like this 
>(untested):
>
>    class MyClass(object):        # ensure a new-style class
>        def __init__(self):
>            self.m_dict = {'one':1, 'two':2, 'three':3}
>        def __getattr__(self, attr):
             try: return self.m_dict[attr]
             except KeyError: raise AttributeError(attr)

>            value = self.m_dict.get(attr, None)
>            if value is None:
>                raise AttributeError(attr)
>            return value
>        def __setattr__(self, attr, value):
>            self.m_dict[attr] = value
>
>I'm using a new-style class to take advantage of improvements in 
>attribute lookup.  For this class, __getattr__()/__setattr__() will only 
>be called if attr isn't found through the normal attribute resolution 
>rules. 
>
>One problem with the way I'm doing things here is that, if you set a 
>dict item to a value of None, the object will raise an AttributeError 
>when trying to access that item.  This really ought to use a safer 
>sentinel value.  (Check for a recent thread here in c.l.py about 
>sentinel values and the use of object() as one.)
>
Why not (untested) avoid the default sentinel and just translate
a key error to an attribute error as above?

Regards,
Bengt Richter