Python中浅拷贝的四种实现方法小结

曾磊

目录

• 方式一：使用切片 [:]
  
• 方式二：使用工厂函数
  
• 方式三：使用数据类型自带的 copy 方法
  
• 方式四：使用 copy 模块的 copy 方法
  

方式一：使用切片 [:]


列表

1. # 浅拷贝 [:]old_list = [1, 2, [3, 4]]new_list = old_list[:]old_list.append(5)old_list[2][0] += 97print("Old list:", old_list, "old list id:", id(old_list), " old list[0] id:", id(old_list[2]))print("new list:", new_list, "new list id:", id(new_list), " new list[0] id:", id(new_list[2]))# 输出结果Old list: [1, 2, [100, 4], 5] old list id: 4537660608  old list[0] id: 4537659840new list: [1, 2, [100, 4]] new list id: 4537711424  new list[0] id: 4537659840

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方式二：使用工厂函数

工厂函数简介

   

• 工厂函数看上去像函数，但实际是一个类   
  
• 调用时，生成该数据类型类型的一个实例
  

可变对象的工厂函数

   

• list()   
  
• set()   
  
• dict()
  

列表

1. old_list = [1, 2, [3, 4]]new_list = list(old_list)old_list.append(5)old_list[2][0] += 97print("Old list:", old_list, "old list id:", id(old_list), " old list[0] id:", id(old_list[2]))print("new list:", new_list, "new list id:", id(new_list), " new list[0] id:", id(new_list[2]))

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集合

1. old_set = {1, 2, 3}new_set = set(old_set)old_set.add(4)print("Old set:", old_set, "old set id:", id(old_set))print("new set:", new_set, "new set id:", id(new_set))# 输出结果Old set: {1, 2, 3, 4} old set id: 4484723648new set: {1, 2, 3} new set id: 4484723872

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字典

1. old_dict = {"name": "小明"}new_dict = dict(old_dict)old_dict["second"] = "Python"print("Old dict:", old_dict, "old dict id:", id(old_dict))print("new dict:", new_dict, "new dict id:", id(new_dict))# 输出结果Old dict: {'name': '小明', 'second': 'Python'} old dict id: 4514161536new dict: {'name': '小明'} new dict id: 4515690304

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方式三：使用数据类型自带的 copy 方法


列表

1. old_list = [1, 2, [3, 4]]new_list = old_list.copy()old_list.append(5)old_list[2][0] += 97print("Old list:", old_list, "old list id:", id(old_list), " old list[0] id:", id(old_list[2]))print("new list:", new_list, "new list id:", id(new_list), " new list[0] id:", id(new_list[2]))# 输出结果Old list: [1, 2, [100, 4], 5] old list id: 4309832000  old list[0] id: 4310372992new list: [1, 2, [100, 4]] new list id: 4309735296  new list[0] id: 4310372992

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集合

1. old_set = {1, 2, 3}new_set = old_set.copy()old_set.add(4)print("Old set:", old_set, "old set id:", id(old_set))print("new set:", new_set, "new set id:", id(new_set))# 输出结果Old set: {1, 2, 3, 4} old set id: 4309931392new set: {1, 2, 3} new set id: 4309930944

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字典

1. old_dict = {"name": "小明"}new_dict = old_dict.copy()old_dict["second"] = "Python"print("Old dict:", old_dict, "old dict id:", id(old_dict))print("new dict:", new_dict, "new dict id:", id(new_dict)) # 输出结果Old dict: {'name': '小明', 'second': 'Python'} old dict id: 4308452288new dict: {'name': '小明'} new dict id: 4308452224

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源码

1. def copy(self, *args, **kwargs): # real signature unknown        """ Return a shallow copy of the list. """        pass

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已经写的很清楚，这是浅拷贝

方式四：使用 copy 模块的 copy 方法


列表

1. from copy import copyold_list = [1, 2, [3, 4]]new_list = copy(old_list)old_list.append(5)old_list[2][0] += 97print("Old list:", old_list, "old list id:", id(old_list), " old list[0] id:", id(old_list[2]))print("new list:", new_list, "new list id:", id(new_list), " new list[0] id:", id(new_list[2]))# 输出结果Old list: [1, 2, [100, 4], 5] old list id: 4381013184  old list[0] id: 4381159936new list: [1, 2, [100, 4]] new list id: 4381012800  new list[0] id: 4381159936

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集合

1. from copy import copyold_set = {1, 2, 3}new_set = copy(old_set)old_set.add(4)print("Old set:", old_set, "old set id:", id(old_set))print("new set:", new_set, "new set id:", id(new_set))# 输出结果Old set: {1, 2, 3, 4} old set id: 4381115552new set: {1, 2, 3} new set id: 4381115776

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字典

1. from copy import copyold_dict = {"name": "小明"}new_dict = copy(old_dict)old_dict["second"] = "Python"print("Old dict:", old_dict, "old dict id:", id(old_dict))print("new dict:", new_dict, "new dict id:", id(new_dict))# 输出结果Old dict: {'name': '小明', 'second': 'Python'} old dict id: 4381159680new dict: {'name': '小明'} new dict id: 4379632576

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