Python中,对象的赋值,拷贝(深/浅拷贝)之间是有差异的,如果使用的时候不注意,就可能产生意外的结果。
下面本文就通过简单的例子介绍一下这些概念之间的差别。
一、对象赋值
又叫变量对对象的引用
li=["Will", 28, ["Python", "C#", "JavaScript"]] new_li=li print(id(li)) #1369658120136 print([id(ele) for ele in li]) #[1369692104328, 1511377424, 1369692110600] print(id(new_li)) #1369658120136 print([id(ele) for ele in new_li]) #[1369692104328, 1511377424, 1369692110600]
可以看出li赋值给了new_li,同时,new_li是引用了li的内存地址
当对数据做修改的操作时:
1、经本人多次试验考证,发现对象赋值,不论多么复杂的数据结构,你对任意数据做了修改之后,都会影响到另一个
2、而且,若数据为可变数据类型,修改数据后,内存地址都不会变
3、若为不可变数据类型,修改数据后,会替换掉旧的对象,即内存地址会发生改变
li=["Will", 28, ["Python", "C#", "JavaScript"]] new_li=li print([id(ele) for ele in li]) #[1925751432840, 1511377424, 1925751446472] li[0] = "Wilber" li[1] = 22 li[2].append("CSS") print ([id(ele) for ele in li]) #[1925751447768, 1511377232, 1925751446472]
二、浅拷贝
import copy li=["Will", 28, ["Python", "C#", "JavaScript",[ {'mm':1}, {'mm':2}, {1,2,3} ]]] new_li=copy.copy(li) print([id(ele) for ele in li]) #[1474180867888, 1511377424, 1474180874120] print([id(ele) for ele in new_li]) #[1474180867888, 1511377424, 1474180874120] new_li[0] = "Wilber" new_li[1] = 22 new_li[2].append("CSS") new_li[2][3][0]='xx' new_li.append('sss') print (li) #['Will', 28, ['Python', 'C#', 'JavaScript', ['xx', {'mm': 2}, {1, 2, 3}], 'CSS']] print ([id(ele) for ele in li]) #[1474180867888, 1511377424, 1474180874120] print (new_li) #['Wilber', 22, ['Python', 'C#', 'JavaScript', ['xx', {'mm': 2}, {1, 2, 3}], 'CSS'], 'sss'] print ([id(ele) for ele in new_li]) #[1474180883040, 1511377232, 1474180874120]
可以看出浅拷贝只拷贝了最外面一层的数据,当对最外面一层做改动时,不会影响到另一个,但是对套在里面的数据做改动就会影响到另外一个。
注:切片的效果和浅拷贝一样
三、深拷贝
import copy li=["Will", 28, ["Python", "C#", "JavaScript",[ {'mm':1}, {'mm':2}, {1,2,3} ]]] new_li=copy.deepcopy(li) print([id(ele) for ele in li]) #[1609895241352, 1511377424, 1609895247752] print([id(ele) for ele in new_li]) #1609895241352, 1511377424, 1609895247816] new_li[0] = "Wilber" new_li[1] = 22 new_li[2].append("CSS") new_li[2][3][0]='xx' new_li.append('sss') print (li) #['Will', 22, ['Python', 'C#', 'JavaScript', [{'mm': 1}, {'mm': 2}, {1, 2, 3}]]] print ([id(ele) for ele in li]) #[1609895241352, 1511377232, 1609895247752] print (new_li) #['Wilber', 28, ['Python', 'C#', 'JavaScript', ['xx', {'mm': 2}, {1, 2, 3}], 'CSS'], 'sss'] print ([id(ele) for ele in new_li]) #[1609895256448, 1511377424, 1609895247816, 1609895256728]
会发现深拷贝对每一层数据都做了拷贝,即对任一数据做了改动,都不会影响到另一个。
四、总结
1、对象赋值是对对象内存地址的引用,它代表原始对象,所以不论对哪一个做了改动,都会影响到另外一个
2、copy.copy()浅拷贝,只对第一层元素进行拷贝
3、若想复制一个容器对象及里面的所有元素(包含元素的子元素),可以使用copy.deepcopy()进行深拷贝
4、对于非容器类型(如数字、字符串、等不可变类型的对象)没有被拷贝一说