python 深浅拷贝

知识点：浅拷贝-->只拷贝第一层 ;  深拷贝-->类似克隆

1.变量赋值  指针的指向完全一样

 列表，字典的内存空间改变，不会重新开辟一个内存空间，所有指针还是一样，两个值都会改变

a = [[1,2],3,4]
>>> b = a
>>> a
[[1, 2], 3, 4]
>>> b
[[1, 2], 3, 4]

>>> b[1] =3333     //修改b的值，a也会放生变化
>>> b
[[1, 2], 3333, 4]
>>> a
[[1, 2], 3333, 4]

字符串，整数型等内存空间改变，会重新开辟一个内存空间存放对象，所以会抹除原来指针，指向新的对象。两个值没关联

>>> a=1
>>> a = 1
>>> b = a
>>> b = 111
>>>
>>> a
1
>>> b
111

 2.浅拷贝

>>> a = [[1,2],3,4]
>>>
>>> b = a.copy()
>>>
>>> a
[[1, 2], 3, 4]    
>>> b
[[1, 2], 3, 4]

>>>
>>> b[1] = 333     //对第一层修改，两者独立
>>> b
[[1, 2], 333, 4]
>>> a
[[1, 2], 3, 4]

>>> b[0][0] = 1111   //对非第一层修改，有关联
>>> b
[[1111, 2], 333, 4]
>>> a
[[1111, 2], 3, 4]

3.深拷贝     两者互相没有任何关联

>>> import copy
>>> 
>>> a = [[1,2],3,4]
>>> b = copy.deepcopy(a)
>>> a
[[1, 2], 3, 4]
>>> b
[[1, 2], 3, 4]
>>> 
>>> a[2] = 444
>>> a
[[1, 2], 3, 444]
>>> b
[[1, 2], 3, 4]
>>> b[0][0] = 111
>>> b
[[111, 2], 3, 4]
>>> a
[[1, 2], 3, 444]