python什么时候用类方法

class Kls(object):

    num_inst = 0

    def __init__(self):

        Kls.num_inst = Kls.num_inst + 1

    @classmethod

    def get_no_of_instance(cls):

        return cls.num_inst

ik1 = Kls()

ik2 = Kls()

print ik1.get_no_of_instance()

print Kls.get_no_of_instance()