==、is
总结
- is 是比较两个引用是否指向了同一个对象（引用比较）。
- == 是比较两个对象是否相等。
深拷贝、浅拷贝
1. 浅拷贝
- 浅拷贝是对于一个对象的顶层拷贝
通俗的理解是：拷贝了引用，并没有拷贝内容
2. 深拷贝
- 深拷贝是对于一个对象所有层次的拷贝(递归)
进一步理解拷贝
In [23]: a = [11,22,33]
In [24]: b = [44,55,66]
In [25]: c = (a,b)
In [26]: e = copy.deepcopy(c)
In [27]: a.append(77)
In [28]: a
Out[28]: [11, 22, 33, 77]
In [29]: b
Out[29]: [44, 55, 66]
In [30]: c
Out[30]: ([11, 22, 33, 77], [44, 55, 66])
In [31]: e
Out[31]: ([11, 22, 33], [44, 55, 66])
In [32]:
In [32]:
In [32]: f = copy.copy(c)
In [33]: a.append(88)
In [34]: a
Out[34]: [11, 22, 33, 77, 88]
In [35]: b
Out[35]: [44, 55, 66]
In [36]: c
Out[36]: ([11, 22, 33, 77, 88], [44, 55, 66])
In [37]: e
Out[37]: ([11, 22, 33], [44, 55, 66])
In [38]: f
Out[38]: ([11, 22, 33, 77, 88], [44, 55, 66])
3. 拷贝的其他方式
浅拷贝对不可变类型和可变类型的copy不同
In [88]: a = [11,22,33]
In [89]: b = copy.copy(a)
In [90]: id(a)
Out[90]: 59275144
In [91]: id(b)
Out[91]: 59525600
In [92]: a.append(44)
In [93]: a
Out[93]: [11, 22, 33, 44]
In [94]: b
Out[94]: [11, 22, 33]
In [95]:
In [95]:
In [95]: a = (11,22,33)
In [96]: b = copy.copy(a)
In [97]: id(a)
Out[97]: 58890680
In [98]: id(b)
Out[98]: 58890680
- 分片表达式可以赋值一个序列
a = "abc"
b = a[:]
- 字典的copy方法可以拷贝一个字典
d = dict(name="zhangsan", age=27)
co = d.copy()
- 有些内置函数可以生成拷贝(list)
a = list(range(10))
b = list(a)
- copy模块中的copy函数
import copy
a = (1,2,3)
b = copy.copy(a)