python 元编程

python

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 2018/06/18   Share

类的创建与销毁

__new__创建类对象实例，__init__初始化类对象实例

class A:
    def __init__(self):
        print(self)
        print('init')

A()
<__main__.A object at 0x10db1f3c8>
init

class A:
    def __new__(cls, *args, **kwargs):
        print('new')
        print(cls)
        return object.__new__(cls)

A()
new
<class '__main__.A'>        #A类对象
<__main__.A at 0x10ded4b00> #A类实例

object.__new__(A)
<__main__.A at 0x10d945320>

object.__new__用于创建对象

class  A:
    def __new__(cls, *args, **kwargs):
        print('new')
        return object.__new__(cls)

    def __init__(self):
        print('init')
        self.x = 3

    def __del__(self):
        print('del')

A()
new
init
<__main__.A at 0x10db82b00>

a=A()
new
init

del a
del

元编程

1	from collections import nametuple
2
3	Person = nametuple('Person', ['name', 'age']) # 神奇之处在于用代码创建了一种新的类型，也就是代码具有写代码的能力

这种能力叫做元编程，通过元编程，我们可以控制类创建的过程

类创建的过程:

成员
继承列表

class DisplayMixin:
    def display(self):
        print(self)

class A(DisplayMixin):
    pass

A().display()
<__main__.A object at 0x10db8a7b8>

debug = True

if debug:
    B = type('B', (DisplayMixin, object), {})
else:
    B = type('B', (), {})

B().display()
<__main__.B object at 0x10d2c2828>


class Meta(type):
    def __new__(cls, name, bases, clsdict):
        new_bases = [DisplayMixin]
        new_bases.extend(bases)
        return super().__new__(cls, name, tuple(new_bases), clsdict)

    def __init__(self, name, bases, clsdict):
        super().__init__(name, bases, clsdict)

class C(metaclass= Meta):
    pass

C().display()
<__main__.C object at 0x10d406ba8>

原文作者：Zhang Jusene

原文链接：http://jusene.github.io/2018/06/18/python-meta/

发表日期：June 18th 2018, 12:07:37 am

更新日期：November 30th 2019, 1:54:24 am

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1. 类的创建与销毁
2. 元编程



缺失模块。
1、请确保node版本大于6.2
2、在博客根目录（注意不是archer根目录）执行以下命令：
npm i hexo-generator-json-content --save
3、在根目录_config.yml里添加配置：

jsonContent:
  meta: false
  pages: false
  posts:
    title: true
    date: true
    path: true
    text: false
    raw: false
    content: false
    slug: false
    updated: false
    comments: false
    link: false
    permalink: false
    excerpt: false
    categories: true
    tags: true

1	class A:
2	def __init__(self):
3	print(self)
4	print('init')
5
6	A()
7	<__main__.A object at 0x10db1f3c8>
8	init
9
10	class A:
11	def __new__(cls, args, *kwargs):
12	print('new')
13	print(cls)
14	return object.__new__(cls)
15
16	A()
17	new
18	<class '__main__.A'> #A类对象
19	<__main__.A at 0x10ded4b00> #A类实例
20
21	object.__new__(A)
22	<__main__.A at 0x10d945320>
23
24	object.__new__用于创建对象
25
26	class A:
27	def __new__(cls, args, *kwargs):
28	print('new')
29	return object.__new__(cls)
30
31	def __init__(self):
32	print('init')
33	self.x = 3
34
35	def __del__(self):
36	print('del')
37
38	A()
39	new
40	init
41	<__main__.A at 0x10db82b00>
42
43	a=A()
44	new
45	init
46
47	del a
48	del

1	class DisplayMixin:
2	def display(self):
3	print(self)
4
5	class A(DisplayMixin):
6	pass
7
8	A().display()
9	<__main__.A object at 0x10db8a7b8>
10
11	debug = True
12
13	if debug:
14	B = type('B', (DisplayMixin, object), {})
15	else:
16	B = type('B', (), {})
17
18	B().display()
19	<__main__.B object at 0x10d2c2828>
20
21
22	class Meta(type):
23	def __new__(cls, name, bases, clsdict):
24	new_bases = [DisplayMixin]
25	new_bases.extend(bases)
26	return super().__new__(cls, name, tuple(new_bases), clsdict)
27
28	def __init__(self, name, bases, clsdict):
29	super().__init__(name, bases, clsdict)
30
31	class C(metaclass= Meta):
32	pass
33
34	C().display()
35	<__main__.C object at 0x10d406ba8>