what is wrong with this property setter

[Peter Otten]

Nagy László Zsolt wrote:

> class Test:
>     def __init__(self):
>         self._parent = None
> 
>     @property
>     def parent(self):
>         return self._parent
> 
>     @parent.setter
>     def set_parent(self, new_parent):
>         self._parent = new_parent
> 
> 
> p, c = Test(), Test()
> c.parent = p
> 
>>py -3 test.py
> 
> Traceback (most recent call last):
>   File "test.py", line 15, in <module>
>     c.parent = p
> AttributeError: can't set attribute

Does this interactive session help you solve it yourself?

$ python3 -i test.py
Traceback (most recent call last):
  File "test.py", line 15, in <module>
    c.parent = p
AttributeError: can't set attribute
>>> [n for n in dir(p) if not n.startswith("_")]
['parent', 'set_parent']
>>> p.set_parent = 42
>>> p.parent
42

Spoiler below if you don't see the light.




























>     @parent.setter
>     def set_parent(self, new_parent):
>         self._parent = new_parent

This creates a settable property with the name "set_parent" and leaves the 
read-only property "parent" alone. To fix your class change the above to

@parent.setter
    def parent(self, new_parent):
        self._parent = new_parent