what's the best way to call a method of object without a guarantee of its existence

[Marco Mariani]

Leon wrote:

> So I need to go back to the module including "parent" class
> to define the objects that I maybe use in future as None,

You can assign them to a placeholder, with a method that always exists 
but does nothing.

class NullObject(object):
     def method(self, *args, **kw):
         pass


> actually, the module including "parent' class works very well
> without those definitions, from parent class's point of view,
> those definitions are kind of noisy.

If you don't feel the need to define the instances there, maybe they 
don't belong to that class after all.