Mixing custom __setattr__ method and properties in new style classes

[Scott David Daniels]

L.C. Rees wrote:
> Can custom __setattr__ methods and properties be mixed in new style
> classes?
> 
> I experimented with a new style class with both a custom __setattr__
> method and a property. Attributes controlled by the __setattr__ method
> work fine. When I attempt to set or get the property it raises the
> error: "TypeError: _settext() takes exactly two arguments (1 given)".
> This suggests that the __setattr__ may be conflicting with assignment
> to the property since it doesn't seem the class name is being passed to
> the property when it's created. This is the code for the property at
> the end of the class definition:
> 
>     def _settext(self, txt):
>         self._tree.text = txt
> 
>     def _gettext(self, txt):
>         return self._tree.text
> 
>     def _deltext(self, txt):
>         self._tree.text = ''
> 
>     text = property(_settext, _gettext, _deltext)
> 
The order to call property is get, set, del, doc
You need to take a _lot_ more care before asking for help.
neither get not del take any arg besides self.  When you are
trying to debug an interaction, make sure your tests work stand-
alone.

     class Holder(object): pass  # to allow attributes stuck on

     class Demo(object):
         def __init__(self):
             self._tree = Holder()

         def _settext(self, txt):
             self._tree.text = txt

         def _gettext(self):
             return self._tree.text

         def _deltext(self):
             self._tree.text = ''

         text = property(_gettext, _settext, _deltext, 'text property')

     d = Demo()
     d.text = 'my text'
     print repr(d.text)
     del d.text
     print repr(d.text)

--Scott David Daniels
scott.daniels at acm.org