class Pet:
    def __init__(self, n, a):
        self._name = n
        self._age = a
    def get_name(self):
        return self._name
    def birthday(self):
        self._age += 1

if __name__ == "__main__":
    cat = Pet("奶茶", 2)
    print(cat.get_name()) # ①
    cat.birthday() # ②
    cat._name = "大橘" # ③
    print(cat.get_name()) # ④