undesired interraction between property and __setattr__

[dman]

On Sat, Jan 26, 2002 at 09:37:54PM +0000, Alex Martelli wrote:
| dman wrote:
|         ...
| >     def __setattr__( self , name , value ) :
| >         if name == "_s" :
| >             self.__dict__[name] = value
| >         elif name in self.__class__.__dict__ :
| >             self.__dict__[ name ] = self.__class__.__dict__[ name ]
| >             self.__dict__[ name ].__set__( self , value )
| >         else :
| >             print name , "=>" , value
| >             setattr( self._s , name , value )
|         ...
| > Is this the proper/ideal solution, or is there something I'm missing,
| > or is this a bug in python?
| 
| I think a somewhat more natural way to code this __setattr__ might be:
| 
|     def __setattr__( self , name , value ) :
|         if name == "_s" or hasattr(
|             getattr(self.__class__, name, None), '__set__'):
|                 object.__setattr__(self, name, value)
|         else :
|             print name , "=>" , value
|             setattr( self._s , name , value )
| 
| i.e.: if the name is _s, OR is the name of a data attribute defined in the
| current class, THEN use the normal way to set the attribute as defined by
| class object (which includes property setting or stashing in self.__dict__),
| ELSE print something and set the name/value attribute in self._s instead.

Thanks.  This is better since (with the proper __getattr__, which has
no unexpected clash) it works with inherited properties as well.

| I find the nested combination of hasattr and setattr here a bit hard to
| follow, though.  My personal preference would be something like:
| 
|     def __setattr__( self , name , value ) :
|         try: setter = self.__class__.name.__set__
                                      ^^^^^^

This would only work in the case
    name == "name"

(unless there's some new magic I'm unaware of :-))

It also isn't recursive, so it wouldn't handle inherited properties.

|         except AttributeError:
|             if name == '_s':
|                 self.__dict__['_s'] = value
|             else:
|                 print name , "=>" , value
|                 setattr( self._s , name , value )
|         else: setter(self, value)
| 
| but it's an issue of personal stylistic preference.


-D

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