Python中浅拷贝的四种实现方法小结

时间:2021-09-26 12:38:02

方式一:使用切片 [:]

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# 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()

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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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原文链接:https://blog.csdn.net/qdPython/article/details/121121358