Python中浅拷贝的四种实现方法小结
时间：2022-09-04 11:20:36|栏目：Python代码|点击： 次
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
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
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
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: 4514161536
new dict: {'name': '小明'} new dict id: 4515690304
方式三：使用数据类型自带的 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
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
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: 4308452288
new dict: {'name': '小明'} 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
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
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
from copy import copy
old_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: 4381159680
new dict: {'name': '小明'} new dict id: 4379632576
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