类的实例化，self

class Person:
    x = 'abc'

    def __init__(self, name, age=19):
        self.name = name
        self.y = age
        #print("pengjai")

    def show(self,y):
        # print(x)
        Person.x = y


tom=Person("jia")
tom.show(2) #self就是实例化对象
Person.show(2,8)  #直接将self当做形参来