How to build Hierarchies of dict's? (Prototypes in Python?)

[Charles D Hixson]

Gabriel Genellina wrote:
>> En Fri, 23 Feb 2007 17:53:59 -0300, Charles D Hixson  
>> <charleshixsn at earthlink.net> escribió:
>>
>>  
>>> I'm sure I've read before about how to construct prototypes in Python,
>>> but I haven't been able to track it down (or figure it out).
>>>
>>> What I basically want is a kind of class that has both class and
>>> instance level dict variables, such that descendant classes
>>> automatically create their own class and instance level dict variables.
>>> The idea is that if a member of this hierarchy looks up something in
>>> it's local dict, and doesn't find it, it then looks in the class dict,
>>> and if not there it looks in its ancestral dict's.  This is rather like
>>> what Python does at compile time, but I want to do it at run time.
>>>     
>>
>> Well, the only thing on this regard that Python does at compile time, 
>> is  to determine whether a variable is local or not. Actual name 
>> lookup is  done at runtime.
>> You can use instances and classes as dictionaries they way you 
>> describe.  Use getattr/setattr/hasattr/delattr:
>>
>> py> class A:
>> ...   x = 0
>> ...   y = 1
>> ...
>> py> class B(A):
>> ...   y = 2
>> ...
>> py> a = A()
>> py> setattr(a, 'y', 3) # same as a.y = 3 but 'y' may be a variable
>> py> print 'a=',vars(a)
>> a= {'y': 3}
>> py>
>> py> b = B()
>> py> print 'b=',vars(b)
>> b= {}
>> py> setattr(b,'z',1000)
>> py> print 'b=',vars(b)
>> b= {'z': 1000}
>> py> print 'x?', hasattr(b,'x')
>> x? True
>> py> print 'w?', hasattr(b,'w')? False
> The trouble is, I'd want to be adding variables at run time.  At 
> least, I *think* that's a problem.  Perhaps I'm misunderstanding what 
> Python's capabilities already are.  How would one write a member 
> function to add a variable to a class?
>
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