Python全栈之路-Day32

1 类的__slots__

#!/usr/bin/env python

# __Author__: "wanyongzhen"

# Date: 2017/4/25

# 只能定义__slots__中规定的属性

#__slots__  用于统一管理所有属性的定义

# 类变量,变量值可以是列表,元祖,或者可迭代对象,也可以是一个字符串(意味着所有实例只有一个数据属性)

class People:

    __slots__ = ['x','y','z']

p = People()

p.x = 1

p.y = 2

p.z = 3

print(p.x,p.y,p.z)

p.v = 4 # 会抛出AttributeError异常

2 迭代器协议

#!/usr/bin/env python

# __Author__: "wanyongzhen"

# Date: 2017/4/25

# __next__ __iter__

from collections import Iterable,Iterator

class Foo:

    def __init__(self,start):

        self.start = start

    def __iter__(self):

        return self

    def __next__(self):

        if self.start > 10:

            raise StopIteration

        num = self.start

        self.start += 1

        return num

f = Foo(0)

print(isinstance(f,Iterable))

print(isinstance(f,Iterator))

print(next(f))

print(next(f))

for item in f:

    print(item)

# 利用迭代特性实现简单的range函数功能

class Range:

    def __init__(self,start,end):

        self.start = start

        self.end = end

    def __iter__(self):

        return self

    def __next__(self):

        if self.start > self.end:

            raise StopIteration

        num = self.start

        self.start += 1

        return num

for item in Range(0,2):

    print(item)

3 类的__del__

#!/usr/bin/env python

# __Author__: "wanyongzhen"

# Date: 2017/4/25

import time

class Open:

    def __init__(self,filepath,mode='r',encode='utf-8'):

        self.f = open(filepath,mode,encoding=encode)

    def write(self):

        pass

    def __getattr__(self, item):

        return getattr(self.f,item)

    def __del__(self):  # 当执行del f(并且引用计数为0时)时会触发这里的函数运行(程序结束时也会运行),一般执行一些清理操作

        print('del func')

        self.f.close()

f = Open('a.txt','w')

del f

time.sleep(5)

4 上下文管理协议

#!/usr/bin/env python

# __Author__: "wanyongzhen"

# Date: 2017/4/25

with open('a.txt','r') as f:

    print('--------->')

    print('--------->')

    print(f.read())

class Foo:

    def __enter__(self):

        print('enter...')

        return self

    def __exit__(self, exc_type, exc_val, exc_tb): # with代码块结束或者出现异常时执行

        print('exit...')

        print('exc_type',exc_type)

        print('exc_val',exc_val)

        print('exc_tb',exc_tb)

        return True  # 处理异常后返回True

with Foo() as f:  # f = Foo().__enter__()

    print('with Foo code area')

    raise TypeError('Error value') # 会调用__exit__

5 元类

#!/usr/bin/env python

# __Author__: "wanyongzhen"

# Date: 2017/4/26

# 元类 type

# 元类(type) --> 类(class) --> 对象(object)

# 1.通常的创建类的方式

class Foo:  #

    x = 1

    def run(self):

        pass

class test:

    pass

print(Foo.__dict__)

print(Foo.__bases__)

print(type(Foo))

# 2.通过元类(type)创建类的方式

def run():

    pass

class_name = 'Foo'

class_bases = (object,)

class_dict = {'x':1,'run':run}

Foo = type(class_name,class_bases,class_dict)

print(Foo.__dict__)

print(Foo.__bases__)

print(type(Foo))

# 元类应用

# 类的函数必须要写注释(__doc__)

class Mymeta(type):

    def __init__(self,class_name,class_bases,class_dict):

        for key in class_dict:

            if callable(class_dict[key]):

                if not class_dict[key].__doc__:

                    raise TypeError('小子,你没写注释,赶紧去写')

class Foo(metaclass=Mymeta):  # Foo = Mymeta('Foo',(object,),{'x':1,'run':run}) 定义时会执行metaclass的__init__

    x = 1

    def __init__(self,name):

        self.name = name

    def run(self):

        'run func'

        print('running')

print(Foo.__dict__)

# 元类实例化过程

class Mymeta(type):

    def __init__(self,class_name,class_bases,class_dict):

        for key in class_dict:

            pass

    def __call__(self, *args, **kwargs):

        print(self)

        obj = self.__new__(self)

        self.__init__(obj,*args,**kwargs)

        return obj

class Foo(metaclass=Mymeta):  # Foo = Mymeta('Foo',(object,),{'x':1,'__init__':__init__,'run':run})  调用Mymeta的__init__

    x = 1

    def __init__(self,name):

        self.name = name

    def run(self):

        'run func'

        print('running')

f = Foo('egon')  # 调用Mymeta的__call__