class Gun:

    def __init__(self, model):

        # 枪的型号
        self.model = model
        # 子弹数量
        self.bullet_count = 0

    def add_bullet(self, count):

        self.bullet_count += count

    def shoot(self):

        # 判断是否还有子弹
        if self.bullet_count <= 0:
            print("没有子弹了...")

            return

        # 发射一颗子弹
        self.bullet_count -= 1

        print("\%s 发射子弹[\%d]..." \% (self.model, self.bullet_count))

# 创建枪对象
ak47 = Gun("ak47")
ak47.add_bullet(50)
ak47.shoot()

class Soldier:

    def __init__(self, name):

        # 姓名
        self.name = name
        # 枪，士兵初始没有枪 None 关键字表示什么都没有
        self.gun = None

    def fire(self):

        # 1. 判断士兵是否有枪
        if self.gun is None:
            print("[\%s] 还没有枪..." \% self.name)

            return

        # 2. 高喊口号
        print("冲啊...[\%s]" \% self.name)

        # 3. 让枪装填子弹
        self.gun.add_bullet(50)

        # 4. 让枪发射子弹
        self.gun.shoot()

>>> a = [1, 2, 3]
>>> b = [1, 2, 3]
>>> b is a 
False
>>> b == a
True