__setattr__ recursion problem

[Hans Nowak]

Joonas Paalasmaa wrote:
> 
> The code above causes an infinite loop. How can I set an attribute of
> Class
> without overloading the __setattr__ function? Or does someone have some
> other
> solution to make that script work?
> 
> class Class2:
>         eggs = 1
>         spam = 2
> 
> class Class:
>         base = Class2()
>         def __setattr__(s,attr, value):
>                 if hasattr(s.base, attr):
>                         setattr(s.base, attr, value)
>                 else:
>                         setattr(s, attr, value)
> 
> Class().foo = "eggs"

The short answer is that setattr(s, ...) calls s.__setattr__.
Which calls setattr again, and so on.

This code strikes me as curious though, and I wonder why you
would want to write it like this. The default idiom for a class
and its subclass would be something like

class Class2:
    def __init__(self):
        self.eggs = 1
        self.spam = 2

class Class(Class2):
    pass

In your approach, 

> class Class:
>         base = Class2()

creates an instance of Class2 *that is shared by all instances
of class*. I'm not sure if this is intentional, but I haven't seen
people use this a lot. Maybe it's possible to rewrite this code
without the setattr and the shared base.

--Hans