Help setting default class attributes

[Steve Holden]

attn.steven.kuo at gmail.com wrote:
> On Sep 6, 10:26 am, rh0dium <steven.kl... at gmail.com> wrote:
>> Hi all,
>>
>> I have the following piece of code and I wanted to set the default
>> attributes based on a dictionary. What I am looking for is a way to
>> take PIPODEFAULTS and assign each one as an attribute for the class
>> pipo.  Can someone show me how to do this by iterating over the
>> PIPODEFAULTS and assign them.  What I would expect to be able to do is
>> call the class and modify them.
>>
>> example:
>> a = pipo()
>> print a.caseSensitivity
>> "preserve"
>>
>> a.caseSensitivity = "lower"
>> print a.caseSensitivity
>> "lower"
>>
> 
> 
> I infer from your example that you want
> to set default attributes for *instances of* class pipo
> (not for class pipo itself).
> 
> Use setattr:
> 
> class pipo(object):
>     PIPODEFAULTS = {'caseSensitivity':'preserve',
>         'cellMapTable':'checkPolygon', # etc
>     }
>     def __init__(self, *args, **kwargs):
>         for attr, value in pipo.PIPODEFAULTS.iteritems():
>             setattr(self, attr, value)
> 
> a = pipo()
> b = pipo()
> print a.caseSensitivity
> a.caseSensitivity = 'lower'
> print a.caseSensitivity
> print b.caseSensitivity
> 
> --
> Hope this helps,
> Steven
> 
> 
This is actually way over-complicated. Remembering that the MRO will 
look in the class to resolve the name of an attribute it doesn't find in 
the instance you can simply use the class as a repository for the defaults:

 >>> class pipo(object):
...     caseSensitivity = 'preserve'
...     cellMapTable = 'checkPolygon'
...     # ...
...
 >>> p1 = pipo()
 >>> p2 = pipo()
 >>> p1.caseSensitivity
'preserve'
 >>> p2.caseSensitivity = "lower"
 >>> p1.caseSensitivity
'preserve'
 >>> p2.caseSensitivity
'lower'
 >>>

You could extend the class to allow per-instance defaults to be set in 
the __init__() method too (untested):

class pipo(object):
     caseSensitivity = "preserve"
     cellMapTable = 'checkPolygon'
     def __init__(self, ..., **kw):
         self.__dict__.update(kw)

p1 = pipo(caseSensitivity='lower')

regards
  Steve
-- 
Steve Holden        +1 571 484 6266   +1 800 494 3119
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