I just realized this while trying to use the openstack command line tools on python3.7. After reading issue33018 and the fact that even in python2

class B:
    pass

def f():
    pass

issubclass(f, B)

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: issubclass() arg 1 must be a class

... I am sure, the new behavior is the correct one. I would be totally fine with closing this issue, and hoping not too many code depend on the strange old behavior :)