Python中浅拷贝的四种实现方法小结

小钢 2021-11-05 09:34:53

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
Oldlist: [1,2, [100,4],5] oldlist id:4537660608  oldlist[0]id:4537659840
newlist: [1,2, [100,4]] newlist id:4537711424  newlist[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
Oldset: {1,2,3,4} oldset id:4484723648
newset: {1,2,3} newset 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
Olddict: {'name':'小明','second':'Python'} olddict id:4514161536
newdict: {'name':'小明'} newdict 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
Oldlist: [1,2, [100,4],5] oldlist id:4309832000  oldlist[0]id:4310372992
newlist: [1,2, [100,4]] newlist id:4309735296  newlist[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
Oldset: {1,2,3,4} oldset id:4309931392
newset: {1,2,3} newset 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
Olddict: {'name':'小明','second':'Python'} olddict id:4308452288
newdict: {'name':'小明'} newdict 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 copyimport 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
Oldlist: [1,2, [100,4],5] oldlist id:4381013184  oldlist[0]id:4381159936
newlist: [1,2, [100,4]] newlist id:4381012800  newlist[0]id:4381159936

集合

from copyimport 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
Oldset: {1,2,3,4} oldset id:4381115552
newset: {1,2,3} newset id:4381115776

字典

from copyimport 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
Olddict: {'name':'小明','second':'Python'} olddict id:4381159680
newdict: {'name':'小明'} newdict id:4379632576