Difference between __getattr__ vs __getattribute__

Question

I am trying to understand when to use __getattr__ or __getattribute__. The documentation mentions __getattribute__ applies to new-sty

Answer 1

In reading through Beazley & Jones PCB, I have stumbled on an explicit and practical use-case for __getattr__ that helps answer the "when" part of the OP's question. From the book:

"The __getattr__() method is kind of like a catch-all for attribute lookup. It's a method that gets called if code tries to access an attribute that doesn't exist." We know this from the above answers, but in PCB recipe 8.15, this functionality is used to implement the delegation design pattern. If Object A has an attribute Object B that implements many methods that Object A wants to delegate to, rather than redefining all of Object B's methods in Object A just to call Object B's methods, define a __getattr__() method as follows:

def __getattr__(self, name):
    return getattr(self._b, name)

where _b is the name of Object A's attribute that is an Object B. When a method defined on Object B is called on Object A, the __getattr__ method will be invoked at the end of the lookup chain. This would make code cleaner as well, since you do not have a list of methods defined just for delegating to another object.