override at runtime __setattr__

Question

I know that in Python it\'s possible to add at runtime a method to a class:

class Test:
    def __init__(self):
        self.a=5

test=Test()

import types
d         


        

Answer 1

It's documented in Data model, section "Class Instances":

Attribute assignments and deletions update the instance’s dictionary, never a class’s dictionary. If the class has a __setattr__() or __delattr__() method, this is called instead of updating the instance dictionary directly.

So no matter if old-style or new-style, those two checks are always made on the type, rather then the instance.