不带参数，等价于 locals().
带参数，等价于 object.__dict__.

class A(object):
    def __init__(self):
        self.a = 1
        self.b = 2

    def keys(self):
        for key in vars(self).keys():
           yield key

    def get_keys(self):
        for key in self.__dict__:
            yield key

a = A()

for key in a.keys():
    print(key)

for key in a.get_keys():
    print(key)


"""
a
b
"""