python3 class attributes scope

Question

class A(object):
    test = 'test'
    d = ['a', 'b']
    [i + test for i in d]

In python2.7, this code works, in python3.6, will report NameError: name 'test' is not defined.

I assume it's related to class attribute working scope change , but haven't found anythings in doc.