四种实现方式实现Python浅拷贝

和天斗

方式一：使用切片 [:]

列表

1. # 浅拷贝 [:]
2. old_list = [1, 2, [3, 4]]
3. new_list = old_list[:]
5. old_list.append(5)
6. old_list[2][0] += 97
8. print("Old list:", old_list, "old list id:", id(old_list), " old list[0] id:", id(old_list[2]))
9. print("new list:", new_list, "new list id:", id(new_list), " new list[0] id:", id(new_list[2]))
12. # 输出结果
13. Old list: [1, 2, [100, 4], 5] old list id: 4537660608  old list[0] id: 4537659840
14. new 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. # 浅拷贝 工厂函数
2. old_list = [1, 2, [3, 4]]
3. new_list = list(old_list)
5. old_list.append(5)
6. old_list[2][0] += 97
8. print("Old list:", old_list, "old list id:", id(old_list), " old list[0] id:", id(old_list[2]))
9. 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. # 浅拷贝 工厂函数-集合
2. old_set = {1, 2, 3}
3. new_set = set(old_set)
5. old_set.add(4)
7. print("Old set:", old_set, "old set id:", id(old_set))
8. print("new set:", new_set, "new set id:", id(new_set))
11. # 输出结果
12. Old set: {1, 2, 3, 4} old set id: 4484723648
13. new set: {1, 2, 3} new set id: 4484723872

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字典

1. # 浅拷贝 工厂函数-字典
2. old_dict = {"name": "小菠萝"}
3. new_dict = dict(old_dict)
5. old_dict["second"] = "测试笔记"
7. print("Old dict:", old_dict, "old dict id:", id(old_dict))
8. print("new dict:", new_dict, "new dict id:", id(new_dict))
11. # 输出结果
12. Old dict: {'name': '小菠萝', 'second': '测试笔记'} old dict id: 4514161536
13. new dict: {'name': '小菠萝'} 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. # 浅拷贝 自带的copy方法-列表
2. old_list = [1, 2, [3, 4]]
3. new_list = old_list.copy()
5. old_list.append(5)
6. old_list[2][0] += 97
8. print("Old list:", old_list, "old list id:", id(old_list), " old list[0] id:", id(old_list[2]))
9. print("new list:", new_list, "new list id:", id(new_list), " new list[0] id:", id(new_list[2]))
12. # 输出结果
13. Old list: [1, 2, [100, 4], 5] old list id: 4309832000  old list[0] id: 4310372992
14. new list: [1, 2, [100, 4]] new list id: 4309735296  new list[0] id: 4310372992

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集合

1. # 浅拷贝 自带的copy方法-集合
2. old_set = {1, 2, 3}
3. new_set = old_set.copy()
5. old_set.add(4)
7. print("Old set:", old_set, "old set id:", id(old_set))
8. print("new set:", new_set, "new set id:", id(new_set))
11. # 输出结果
12. Old set: {1, 2, 3, 4} old set id: 4309931392
13. new set: {1, 2, 3} new set id: 4309930944

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字典

1. # 浅拷贝 自带的copy方法-字典
2. old_dict = {"name": "小明"}
3. new_dict = old_dict.copy()
5. old_dict["second"] = "python"
7. print("Old dict:", old_dict, "old dict id:", id(old_dict))
8. print("new dict:", new_dict, "new dict id:", id(new_dict))
11. # 输出结果
12. Old dict: {'name': '小明', 'second': 'python'} old dict id: 1611676464896
13. new dict: {'name': '小明'} new dict id: 1611676464960

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源码

1. def copy(self, *args, **kwargs): # real signature unknown
2.     """ Return a shallow copy of the list. """
3.     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. # 浅拷贝 copy模块的copy方法-列表
2. from copy import copy
4. old_list = [1, 2, [3, 4]]
5. new_list = copy(old_list)
7. old_list.append(5)
8. old_list[2][0] += 97
10. print("Old list:", old_list, "old list id:", id(old_list), " old list[0] id:", id(old_list[2]))
11. print("new list:", new_list, "new list id:", id(new_list), " new list[0] id:", id(new_list[2]))
14. # 输出结果
15. Old list: [1, 2, [100, 4], 5] old list id: 4381013184  old list[0] id: 4381159936
16. new list: [1, 2, [100, 4]] new list id: 4381012800  new list[0] id: 4381159936

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集合

1. # 浅拷贝 copy模块的copy方法-集合
2. from copy import copy
4. old_set = {1, 2, 3}
5. new_set = copy(old_set)
7. old_set.add(4)
9. print("Old set:", old_set, "old set id:", id(old_set))
10. print("new set:", new_set, "new set id:", id(new_set))
13. # 输出结果
14. Old set: {1, 2, 3, 4} old set id: 4381115552
15. new set: {1, 2, 3} new set id: 4381115776

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字典

1. # 浅拷贝 copy模块的copy方法-字典
2. from copy import copy
4. old_dict = {"name": "小明"}
5. new_dict = copy(old_dict)
7. old_dict["second"] = "python"
9. print("Old dict:", old_dict, "old dict id:", id(old_dict))
10. print("new dict:", new_dict, "new dict id:", id(new_dict))
13. # Python小白学习交流群：153708845
14. # 输出结果
15. Old dict: {'name': '小明', 'second': 'python'} old dict id: 3220382234368
16. new dict: {'name': '小明'} new dict id: 3220382234432

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来源:https://www.cnblogs.com/djdjdj123/p/17782917.html
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