class Student:
    count=0
    
    def __init__(self,name,age):
        self.name=name
        self.age=age
        Student.count+=1  # 要使得变量全局有效，就定义为类的属性
    def learn(self):
        
        print(self.name+'is learning')

stu1 = Student("jack", 33)

stu1.learn()
stu2 = Student("amy", 24)
stu2.learn()

stu3 = Student("lucy", 22)
stu3.learn()

stu4 = Student("lulu", 45)
stu4.learn()


print("实例化了%s个学生" % Student.count)