Python - 浅拷贝的四种实现方式
浅拷贝详解
https://www.cnblogs.com/poloyy/p/15084277.html
方式一：使用切片 [:]
列表
# 浅拷贝 [:] old_list = [1, 2, [3, 4]] new_list = old_list[:] old_list.append(5) old_list[2][0] += 97 print("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: 4537659840 new list: [1, 2, [100, 4]] new list id: 4537711424 new list[0] id: 4537659840
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
# 浅拷贝 工厂函数 old_list = [1, 2, [3, 4]] new_list = list(old_list) old_list.append(5) old_list[2][0] += 97 print("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]))
集合
# 浅拷贝 工厂函数-集合 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: 4484723648 new set: {1, 2, 3} new set id: 4484723872
字典
# 浅拷贝 工厂函数-字典 old_dict = {"name": "小菠萝"} new_dict = dict(old_dict) old_dict["second"] = "测试笔记" 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': '小菠萝', 'second': '测试笔记'} old dict id: 4514161536 new dict: {'name': '小菠萝'} new dict id: 4515690304
方式三：使用数据类型自带的 copy 方法
列表
# 浅拷贝 自带的copy方法-列表 old_list = [1, 2, [3, 4]] new_list = old_list.copy() old_list.append(5) old_list[2][0] += 97 print("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: 4310372992 new list: [1, 2, [100, 4]] new list id: 4309735296 new list[0] id: 4310372992
集合
# 浅拷贝 自带的copy方法-集合 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: 4309931392 new set: {1, 2, 3} new set id: 4309930944
字典
# 浅拷贝 自带的copy方法-字典 old_dict = {"name": "小菠萝"} new_dict = old_dict.copy() old_dict["second"] = "测试笔记" 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': '小菠萝', 'second': '测试笔记'} old dict id: 4308452288 new dict: {'name': '小菠萝'} new dict id: 4308452224
源码
def copy(self, *args, **kwargs): # real signature unknown """ Return a shallow copy of the list. """ pass
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
# 浅拷贝 copy模块的copy方法-列表 from copy import copy old_list = [1, 2, [3, 4]] new_list = copy(old_list) old_list.append(5) old_list[2][0] += 97 print("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: 4381159936 new list: [1, 2, [100, 4]] new list id: 4381012800 new list[0] id: 4381159936
集合
# 浅拷贝 copy模块的copy方法-集合 from copy import copy old_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: 4381115552 new set: {1, 2, 3} new set id: 4381115776
字典
# 浅拷贝 copy模块的copy方法-字典 from copy import copy old_dict = {"name": "小菠萝"} new_dict = copy(old_dict) old_dict["second"] = "测试笔记" 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': '小菠萝', 'second': '测试笔记'} old dict id: 4381159680 new dict: {'name': '小菠萝'} new dict id: 4379632576
