1class A:
2    def __bool__(self):
3        print('__bool__')
4        return True
5    def __len__(self):
6        print('__len__')
7        return 1
8
9class B:
10    def __len__(self):
11        print('__len__')
12        return 0
13
14print(bool(A()))
15print(len(A()))
16print(bool(B()))
17print(len(B()))
18