Python 深浅拷贝

Python 深浅拷贝

http://www.cnblogs.com/aylin/p/5467506.html

a、数字和字符串

    对于数字和字符串而言，赋值、浅拷贝和深拷贝无意义，因为其永远指向同一个内存地址。

>>> import copy
>>> a = 123
>>> id(a)
9027904
>>> b = a
>>> id(b)
9027904
>>> a1 = copy.copy(a)
>>> a1
123
>>> id(a1)
9027904
>>> a2 = copy.deepcopy(a)
>>> id(a2)
9027904
>>>

b、其他基本数据类型

对于字典、元祖、列表 而言，进行赋值、浅拷贝和深拷贝时，其内存地址的变化是不同的。

赋值，只是创建一个变量，该变量指向原来内存地址

浅拷贝，在内存中只额外创建第一层数据

 

深拷贝，在内存中将所有的数据重新创建一份（排除最后一层，即：python内部对字符串和数字的优化）

>>> a1 = [1,2,3]
>>> a2 = a1
>>> import copy
>>> a3 = copy.copy(a1)
>>> a4 = copy.deepcopy(a1)  
>>> id(a1)
140065463143048
>>> id(a2)
140065463143048
>>> id(a3)
140065462442632
>>> id(a4)
140065460223752
>>> a1
[1, 2, 3]
>>> a2
[1, 2, 3]
>>> a3
[1, 2, 3]
>>> a4
[1, 2, 3]
>>>
>>> a1.append(4)
>>> a1
[1, 2, 3, 4]
>>> a2
[1, 2, 3, 4]
>>> a3
[1, 2, 3]
>>> a4
[1, 2, 3]
>>> id(a1)
140065463143048
>>> id(a2)
140065463143048
>>> id(a3)
140065462442632
>>> id(a4)
140065460223752
>>>

>>> b1 = {'x':'111','y':'222'}
>>> type(b1)
<class 'dict'>
>>> b2 = b1
>>> b3 = copy.copy(b1)
>>> b4 = copy.deepcopy(b1) 
>>> id(b1)
140065460223816
>>> id(b2)
140065460223816
>>> id(b3)
140065457735880
>>> id(b4)
140065463642952
>>> b1
{'x': '111', 'y': '222'}
>>> b1['z'] = '333'
>>> b1
{'x': '111', 'y': '222', 'z': '333'}
>>> b1['x'] = '444' 
>>> b1
{'x': '444', 'y': '222', 'z': '333'}
>>>       
... 
>>> b1
{'x': '444', 'y': '222', 'z': '333'}
>>> b2
{'x': '444', 'y': '222', 'z': '333'}
>>> b3
{'x': '111', 'y': '222'}
>>> b4
{'x': '111', 'y': '222'}
>>>   
>>> id(b1)                    
140065460223816
>>> id(b2)
140065460223816
>>> id(b3)
140065457735880
>>> id(b4)
140065463642952
>>>