Python面向对象进阶（二）

Python面向对象进阶2.html

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---

title: Python 面向对象进阶2
tags: Python

• • 1 setitem getitem delitem

    
    0

  • 2 _slots_

    
    1

  • 3 _next和 \iter_ 实现迭代器协议

    
    2

  • 4 _doc_

    
    3

  • 5 _module 和 \class_

    
    4

  • 6 _del_ 析构方法

    
    5

  • 7 _enter 和 exit_上下文管理协议

    
    6

1 setitem getitem delitem

把 对象操作属性模拟字典格式

class Foo:
    def __init__(self,name):
        self.name=name
    def __getitem__(self, item):
        return self.__dict__[item]  # getitem 通过return返回
    def __setitem__(self, key, value):
        self.__dict__[key]=value     # 真正操作的是字典中的
    def __delitem__(self,key):
        # self.__dict__.pop[key]  # 把字典中的删除
        self.__dict__.pop(key)  # pop是个函数

f=Foo('aaa')  # 实例化
print(f['name']) # 这是getitem
f['age']=18  # setitem
print(f.__dict__)

打印结果：
{‘name’: ‘aaa’, ‘age’: 18}

f=Foo('aaa')
print(f['name'])
f['age']=18
del f['age']    # delitem
del f['name']
print(f.__dict__)  # 通过查看对象的名称空间可

结果:

2 _slots_

slots是一个类变量，变量的值可以是列表、字典、字符串、可迭代对象,用的是类的名称空间，是共享的，对象没有自己的名称空间，省内存

class People:
    __slots__=['x','y','z']  #设置相应的属性
p=People()
print(People.__dict__)
p.x=1
p.y=2
p.z=3
print(p.x,p.y,p.z)
# print(p.__dict__)
p1=People()
p1.x=11
p1.y=21
p1.z=31
print(p1.x,p1.y,p1.z)

结果：
1 2 3
11 21 31

slots应用：字典会占用大量内存，如果一个类的属性很少，但是有很多类，为了节省内存可以使用slots代替dict

3 __next和 ___iter__ 实现迭代器协议

可迭代对象内置iter方法，可迭代对象赋值就是一个迭代器，迭代器可以使用next方法

from collections import Iterator,Iterable
class Foo:
    def __init__(self,start):
        self.start=start
    def __iter__(self):
        return self
    def __next__(self):
        if self.start > 10:
            raise StopIteration
        n = self.start
        self.start+=1
        return n

f=Foo(5)
# print(next(f))
for i in f:
    print(i)

4 _doc_

class Foo:
    '这是描述信息'
    pass
print(Foo.__doc__)    # 打印的结果就是函数的注释信息

无法继承

class Foo:
    '这是描述信息'
    pass
class Bar(Foo):
    pass
print(Bar.__dic__)

结果：
type object ‘Bar’ has no attribute ‘dic‘

5 _module 和 __class__

module 表示当前操作的对象在那个模块

class 表示当前操作的对象的类是什么

class Foo:
    '这是描述信息'
    pass
class Bar(Foo):
    pass
# print(Bar.__dic__)
b=Bar()
print(b.__module__)
print(b.__class__)
print(Bar.__class__)
print(Foo.__class__)

结果：
main
class ‘main.Bar’>
class ‘type’>
class ‘type’>

6 _del_ 析构方法

但对象在内存中被释放时，自动触发_del_

class Foo(object):
    """docstring for Foo"""
    def __del__(self):
        print("zhi xing ")
f1 = Foo()
del f1
print('----')

文件操作

class Open:
    def __init__(self,filepath,mode='r',encoding='utf-8'):
        self.x = open(filepath,mode=mode,encoding=encoding)
        # self.x = open(filepath,mode=mode,encoding=encoding)
        self.filepath =filepath
        self.mode=mode
        self.encoding=encoding
    def write(self,line):
        self.x.write(line)
    def __getattr__(self, item):
        return getattr(self.x,item)
    def __del__(self):
        self.x.close()
f=Open('a.txt','w')
del f

7 __enter__ 和 __exit__上下文管理协议

上下文管理协议，即with语句，为了让一个对象兼容with语句必须在对象中声明enter 和iter