Simple class attribute spy for Python

spy.py

class Spy:

    # replace getattr of class and collect all calls
    # and the return the underlying class' getattr
    def __init__(self, cls):
        self.spy_on = cls.__name__
        self.cls_getattr = cls.__getattribute__
        self.cls_getitem = cls.__getitem__
        self.attributes_read = set()
        self.items_read = set()
        def spy_getattribute(instance, attr):
            self.attributes_read.add(attr)
            return (self.cls_getattr)(instance, attr)
        def spy_getitem(instance, item):
            self.items_read.add(item)
            return (self.cls_getitem)(instance, item)
        cls.__getattribute__ = spy_getattribute
        cls.__getitem__ = spy_getitem

    def report(self):
        return f"""
Spied on {self.spy_on}.
These attributes were read:
{', '.join(sorted(self.attributes_read))}
These items were read:
{', '.join(sorted(self.items_read))}
"""