### 测试 pickle 功能的代码，卸载装入多个对象
import pickle

class B:
    def __init__(self, a): self._a = a + 1
    def prt(self, name): print(name + ':', self._a)

x = B(3); y = B(5) # 创建两个对象
x.prt("x"); y.prt("y")   # 检查它们的内容

with open('pickle.pickle', 'wb') as f: # 把两个对象顺序卸载到文件
    pickle.dump(x, f)
    pickle.dump(y, f)

del x, y # 销毁前面创建的对象

with open('pickle.pickle', 'rb') as f: # 顺序装入前面卸载的对象
    a = pickle.load(f)
    b = pickle.load(f)

print("\nData after pickle and unpickle:")
a.prt("a")
b.prt("b")