《Core Python 2nd》读书摘要二

21.标准Type的分类
作者将标准Type分成三个Model，以搞清相互之间的关系，以及如何动作。

①Storage Model：

Storage Model Category	Python Types That Fit Category
Scalar/atom	Numbers (all numeric types), strings (all are literals)
Container	Lists, tuples, dictionaries

String不被看成Container是因为没有Character这个基本Type。

 

②Update Model：

Update Model Category	Python Types That Fit Category
Mutable	Lists, dictionaries
Immutable	Numbers, strings, tuples

Number和String也是Immutable，尽管如下语句：

x = 'Python numbers and strings'
x = 'are immutable?!? What gives?'
i = 0
i = i + 1

但其实x、i并非被更改了值，而是系统生成了新的对象，然后将x、i指向这个新的对象，原来的对象将被垃圾回收。通过查看id(x)可以看出其前后的差别。

 

③Access Model：

Access Model Category	Python Types That Fit Category
Direct	Numbers
Sequence	Strings, lists, tuples
Mapping	Dictionaries

 

综合：

Data-Type	Storage-Model	Update-Model	Access-Model
Numbers	Scalar	Immutable	Direct
Strings	Scalar	Immutable	Sequence
Lists	Container	Mutable	Sequence
Tuples	Container	Immutable	Sequence
Dictionaries	Container	Mutable	Mapping