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'''
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命令模式（Command Pattern）是一种行为设计模式，它封装了一个请求作为一个对象，从而让你使用不同的请求把客户端与服务端操作解耦。在书城的业务背景中，命令模式可以用来实现例如添加购物车项、结算订单、发送通知等操作。
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下面是一个简单的使用Python实现的命令模式示例，以书城的购物车操作为例
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'''
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# 购物车类
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class ShoppingCart:
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def __init__(self):
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self.items = []
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def add_item(self, book_id, quantity):
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self.items.append({'book_id': book_id, 'quantity': quantity})
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print(f"Added {quantity} of book ID {book_id} to the cart.")
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def remove_item(self, book_id):
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self.items = [item for item in self.items if item['book_id'] != book_id]
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print(f"Removed book ID {book_id} from the cart.")
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# 命令接口
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class Command:
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def execute(self):
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pass
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# 具体命令类 - 添加购物车项
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class AddToCartCommand(Command):
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def __init__(self, shopping_cart, book_id, quantity):
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self.shopping_cart = shopping_cart
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self.book_id = book_id
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self.quantity = quantity
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def execute(self):
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self.shopping_cart.add_item(self.book_id, self.quantity)
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# 具体命令类 - 移除购物车项
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class RemoveFromCartCommand(Command):
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def __init__(self, shopping_cart, book_id):
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self.shopping_cart = shopping_cart
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self.book_id = book_id
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def execute(self):
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self.shopping_cart.remove_item(self.book_id)
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# 调用者（Invoker）类
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class Invoker:
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def __init__(self):
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self.commands = []
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def store_and_execute_command(self, command):
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self.commands.append(command)
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command.execute()
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# 客户端代码
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if __name__ == "__main__":
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cart = ShoppingCart()
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invoker = Invoker()
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# 创建添加购物车项命令
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add_command = AddToCartCommand(cart, "12345", 2)
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invoker.store_and_execute_command(add_command)
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# 创建移除购物车项命令
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remove_command = RemoveFromCartCommand(cart, "12345")
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invoker.store_and_execute_command(remove_command)
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'''
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在这个例子中，我们有一个ShoppingCart类，它有两个方法：add_item和remove_item，用于添加和移除购物车项。然后，我们定义了一个命令接口Command和一个调用者Invoker。Invoker可以存储并执行命令。
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具体命令类AddToCartCommand和RemoveFromCartCommand实现了Command接口，并在execute方法中调用了ShoppingCart的相应操作。
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客户端代码创建了ShoppingCart实例和Invoker实例，并创建了添加和移除购物车项的具体命令对象。这些命令对象通过调用者的store_and_execute_command方法被存储和执行。
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这个命令模式的实现将购物车操作和实际的执行逻辑解耦，允许客户端在不知道具体操作的情况下存储和执行命令。这对于支持撤销操作、记录命令历史、排队命令等高级功能非常有用。
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'''
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