Demonstra getitem/setitem

example.py

class Getitem(object):
    def __init__(self, a):
        self.a = a
    def __getitem__(self, attr):
        print(f"__getitem__ {attr}")
        return getattr(self, attr)


class Setitem(Getitem):
    def __setitem__(self, attr, value):
        print(f"__setitem__ {attr} {value}")
        return setattr(self, attr, value)


class Add(object):
    def __add__(self, value):
        print(f"__add__     {value}")
        return self


s = Setitem(Add())

print("s.a access")
s.a    += 1

print("s[a] access")
s["a"] += 1

g = Getitem(Add())

print("g.a access")
g.a    += 1

print("g[a] access")
g["a"] += 1