[Tutor] set/getattr and inheritance

[Lloyd Kvam]

You are responsible for managing the "inheritance" issues when you use __getattr__ and __setattr__.  __setattr__ is the one that's very hard to get correct.  I have cheated and used my own routine, normally called set, as an alternative to writing
__setattr__.  This set method then searches for the correct dictionary to use.  setattr continues to work with the regular class dictionary.

There may well be smarter solutions.

Run-Sun Pan wrote:
> 
> Hi all,
> 
> I am using the __setattr__ and __getattr__ pair
> to access variables of my class:
> 
> #-------------------------
> class c_template():
>   myAddr = 'blahblahblah'
> 
> class c_myclass(c_template):
>   def __init__(self):
>     self.__dict__['vars']={}
>     self.vars['myName']='pan'
> 
>   def __setattr__(self,name,value):
>     if not self.vars.has_key(name): raise AttributeError
>     self.vars[name]=value
> 
>   def __getattr__(self,name):
>     if not self.vars.has_key(name): raise AttributeError
>     return self.vars[name]
> 
> mc = c_myclass()
> mc.myName='panpan'
> mc.myAddr='blah' # trying to use the var of ancestor c_template
> #---------------------------
> 
> The last line of code raises an AttributeError. It's
> quite obvious that this .myAddr is not in the "vars"
> variable list of the current class (c_myclass), thus
> an error occurs.
> 
> I can overcome this by redefining the c_myclass as:
> 
>  class c_myclass(c_template):
>    def __init__(self):
>      myName='pan'
> 
> or simply:
> 
>   class c_myclass(c_template):
>      myName='pan'
> 
> which means, bypassing the usage of __setattr__,
> __getattr__ pairs. But then I can't utilize their
> functions to check the input values before they
> are assigned / obtained.
> 
> Is there anyway to use these setattr/getattr pair
> yet still be able to access ancestor's variables ?
> 
> thx in advance.
> 
> pan
> 
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-- 
Lloyd Kvam
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