class Employee:
    def __init__(self, name, salary, age = -1):
        self.name = name
        self.salary = salary
        self.age = age

    def printclass(self):
        if(self.age == -1):
            print("Error! No age")
        else:
            print(f"{self.name}'salary is {self.salary}, and his age is {self.age}")

name = input()
salary = input()
e = Employee(name, salary)
e.printclass()
age = int(input())
e.age = age
e.printclass()

属性是可以动态的添加的,在最开始init的时候可以没有age的属性。如果要添加,可以直接e.age这样就可以直接添加了