class item assignment python

class ItemAssign():
# initialize
    def __init__(self, a, b):
        self.a = a
        self.b = b
# set item
    def __setitem__(self, k, v):
        if k == "a":
            self.a = v
        if k == "b":
            self.b = v
# get item
    def __getitem__(self, k):
        if k == "a":
            return self.a
        if k == "b":
            return self.b
# len
    def __len__(self):
        return 2
# del item
    def __delitem__(self, k):
        self[k] = None
# instance = ItemAssign(2, 4)
# for x in instance:
    def __iter__(self):
        yield self.a
        yield self.b